Didn't play in PUBD or anything, so take this with a grain of salt, but played about 20 tour games between FC and RoA ST & topped the PU RoA ladder (meaningless but we love a bit of bad-faith flexing), so figured I'd drop my thoughts on all the mons I think have any sort of place post-VL. Apologies for the ensuing 32-mon yap session.
S TIER — Play every game assuming you'll see these mons
Golduck &
Rapidash
I think Golduck and Rapidash are pretty interchangeable for the top spot, and the only mons in the tier you should really expect to see on every single team, though some talented folks have found success on teams without them. Golduck is often spent fighting itself, but being one of the only safe golduck switch-ins in the tier outside of *maybe* Staryu is great, and it threatens any non-water type with immediate big damage. Amnesia isn't the scary sweeping tool it once was in NU with how fast and physically offensive current PU is, but it serves as a great answer to stallers like Porygon in a pinch, and to a lesser extent Staryu. Rapidash is one of the safest revenge killers out there, outspeeds everything, hits almost everything for solid damage, threatens para with body slam, threatens lategame cheese and emergency pivoting utility with fire spin, it really has everything you'd want.
Porygon
The undisputed stall king of PU. Twave+recover gives it incredible chipping potential against anything that can't do more than 50% per hit (which is most of the tier). Unless something else switches in and paralyzes/sleeps it, Porygon completely shuts down Seaking, Pidgeot, Magmar, Graveler, and Counter-Golduck, and puts other high tier mons like Rapidash, Scyther, and Primeape in a tough spot, because even though they can technically break pory with fire spin/SD/Submission, they really don't like eating a para. The 'gon also has the best set diversity in PU, with access to Blizz/Psychic/TBolt/Agility/Hyper Beam/DEdge/& Sharpen(lol) to round out its final 2 moves. There's a configuration of Porygon that beats just about every single mon in the tier with a little bit of luck. Though not the best duck in PU, it's probably responsible for the most single-handedly won endgames if nothing's able to break it.
A TIER — They have a consistently useful role and fill it well
Pidgeot &
Scyther
These mons fill very similar roles on a team as a fast revenge killer that can hit anything besides Gastly and the rocks for big damage, and I think they're both roughly as good as each other. Pidgeot is a bit more consistent in my eyes, as it's more immediately threatening thanks to STAB, and you can play more recklessly with it and get more value throughout the course of a game. Using Scyther in the early/midgame reveals that you have one, and your opponent will take extra care not to let themselves get to a position where you can set up SD and clean house. Scyther has access to more tools and is faster, but most of the time I prefer using Pidgeot because it can be used at any point in the game without losing value.
Nidoking
Nido at #6 is something I went back and forth on, as I think there's an argument for him as high as 4 or as low as 9. He's extremely plug-and-play, and goes roughly 1-for-1 on most things in the tier. Probably the 2nd most consistent lead in the tier (slightly below Magmar), and whenever I drop him, I end up wishing I had him as a reliable option in almost every endgame.
Magmar
Probably the most consistent lead in the tier. Psychic has a >50% chance to beat Nidoking, HBeam ohkos Abra, FBlast hits Venusaur for like 75%, Rapidash doesn't want to risk BSlam para, and if you see the odd lead Golduck you can switch to your own Golduck and still trade roughly 1-for-1. Magmar isn't going to pidgeonhole you as a lead no matter what you see. It also works well mid/lategame as a fast revenge killer, and a decent option to fight a lategame rapidash with BSlam paras or counter.
Abra
I still don't love using Abra, but I can't deny that it has a great role as a solid attacker that outspeeds Nidoking/Golduck/Venusaur/Gastly, very little wants to switch in on it, can spread para with twave, and it works as a decent answer to the most common Porygon set (twave/recover/psychic/agility). Even if it dies to every fast attacker with a normal type attack, it makes a very consistent early/midgame piece, and its PUBD usage reflects that, at #5 most commonly-brought mon.
B1 TIER — They fill helpful roles, but are inconsistent
Seaking
Definitely the best B tier mon, the amount of high-level matches that end in the "Seaking agility" into "sweep everything left on the field" combo make it an obvious win condition and a dangerous threat. But depending on the endgame you're left with, plenty of matches end with a Seaking that does very little and then dies, and Porygon needs to be out of the picture before Seaking tries to sweep. It needs the right conditions to thrive, and players better than I can get scarily good value out of it.
Gastly
The best sleeper in the tier imo. Shuts down any Pidgeot/Scyther without a flying move (plenty of them run either sand attack or agility as their optional moves, so this is quite common), and can still provide tempo in a neutral-to-bad matchup if it gets lucky with Hypnosis or boom. It's just a bit too frail in the new meta, has a slightly unfavorable venusaur matchup (speed tie + less accurate sleep move) and dies if Nidoking looks at it funny.
Primeape
A solid revenge killer that outspeeds other common revenge killers like Pidgeot/Magmar/Abra. It's worse than all of them at being a standard revenge killer, but its speed tier gives it an edge at revenging them back. Unlike them, it can also threaten a kill on a chipped Porygon using Submission (does around 75% damage), and doesn't get walled by Graveler the way Pidg/Scyther do.
Venusaur
Looks amazing at first glance, but actually kinda sucks if you use it long enough. It's very bulky and has the most consistent sleep, but it really struggles to do much once sleep is off the table. It doesn't get double powder, it's too slow to safely answer Golduck with razor leaf, and the fires clobber you, since you've usually eaten 40% before landing sleep in the first place. Best value imo is immediately trying to sleep something, then fishing for body slam paras on whatever comes in. Pidgeot really shuts it down post-sleep as a result, and Scyther likes setting up on it since bslam doesn't break sub.
Graveler
Being a big bulky rock type gives it incredibly polarizing matchups in this meta. Everything outspeeds it, and anything with a super effective move pretty much one-shots it. It does however completely shut down Pidgeot/Scyther which is super helpful given how immediately threatening they are, and threatens solid damage with EQ/RSlide/Boom on most everything else. It really wishes it didn't have to worry about FBlast burns, because it can be a very scary threat to a Rapidash or Magmar, and it really can't safely switch in on either of them unless you're confident a hyper beam is coming your way.
B2 TIER — Koolaid I'm drinking
Staryu
Staryu wishes Porygon wasn't around to outclass it, but it does appreciate most of the mons that dropped from NU. Can threaten twave + tbolt on Golduck (though amnesia is unfortunate for it), threatens twave+surf on Rapidash, totally shuts down Seaking, threatens to paralyze the fast revenge killers, it's got all the trappings of a great mon. But in my experience it's tough to slot 2 fairly-slow stall mons on the same team, and Porygon just fills this role better. And it seems the high-level players agree, as Porygon was used 4x as much as Staryu in tour.
Pinsir &
Machamp
Two mons that can threaten solid damage on most of the tier and have decent bulk, but they're unfortunately both outcompeted by Nidoking now. If you want something you can safely go 1-for-1 with, just bring Nido. Pinsir hates that Rapidash and Magmar are so often healthy lategame, and Machamp is just slow as dirt. Both do have a niche as lategame Porygon answers with Swords Dance & Submission, but they're sort of a weird hybrid of Nidoking and Primeape that don't have the high points of either of them. They usually put in work, but it's hard to justify them over mons higher on this list.
Wigglytuff
I'll be real, my wigglytuff stocks dropped from like high B1 to almost C as the meta developed. On paper, it's incredibly bulky, has access to a sleep move to take advantage of that bulk, can spread paralysis, packs blizzard/tbolt/bslam/hbeam for solid damage, has sky-high HP to make counters hit like a truck, it's got so much going for it. So why is it so ass? It underperforms consistently in all the matches I've seen it used in. It doesn't have Chansey level bulk against anything, so going for sing is very inconsistent. Twave is nice, but Porygon/Abra/Staryu do it better. It's slow as dirt, so even if it hits for decent damage, it can only do it 2-3 times before it dies, since it doesn't have recovery outside of rest. I wish it were better, and it definitely has the potential to rise for me if I see it perform well, but so far it's just not there.
Drowzee
Drowzee at B2 might seem way too high, but I think he has a surprisingly good matchup spread. He can safely switch into Abra & Porygon without risking much damage (at least until pory users stop packing exclusively psychic as their only damaging move), and Drowzee beats both of them 1v1. Abra seismic toss is a 4hko, while Drowzee headbutt is often a 3hko, or you could pack Mega Kick for a guaranteed 2hko if you're cool. Hypnosis is incredibly threatening if Drowzee gets onto the field against an abra/pory, and since it's already slow as dirt it doesn't fear eating a para. Plus if you're really wacky, counter OHKOs pidgeot regardless of what attacking move it uses.
Omanyte
Is Omanyte at B2 probably very stupid and *definitely* indicative of bias? No, I would never suggest that. But hypothetically if it WAS pure cope that it's this high, let me defend it a bit. As a rock type that only really attacks specially, it doesn't have to worry about burn the same way Graveler does. It can safely switch in on Rapidash/Pidgeot/Scyther, and unlike ZU, Magmar doesn't run seismic toss all that often, so you can switch in on Magmar pretty reliably as well. It doesn't hit very hard outside of decent water/ice attacks, and is slow as bricks, so it only shines as a counter in endgames, but given how often endgames have a Rapidash/Pidgeot/Scyther/Magmar, your odds of getting good milage out of this thing is quite high. Hates tf out of Seaking endgames tho.
C TIER — Koolaid I'm not drinking (yet)
Kingler
My crab agenda can only elevate this thing so far. While it can hit most things for solid damage and is one of the few mons that can break an endgame porygon, this thing is just too slow for this meta. It doesn't work very well early/midgame, it eats decent damage if it ever tries to switch in or revenge something, if your opponent has Venusaur it's the freest switch of all time, it's just rough. I want this mon to do well, and I think it has the potential to work as a lategame mon with some developments and move up to B2, but so far it's way outclassed by Seaking.
Exeggcute
Incredibly slow and hates the prevalence of fire types and blizzard users. It has boom which is nice, and its psychic typing gives it a niche against monopsy/psybolt pory and abra, but it's just tough to slot. Might be the Drowzee koolaid talking, but I'm taking the stupid tapir way before I take the egg.
Sandslash
Has a lot of potential as a monopsy/psybolt Porygon punish, and can find solid entry points against twave/tbolt users like pory/abra/gastly/staryu/drowzee. It can hit quite hard, can set up even further with SD, and not too much wants to switch into it once it's out, but like Kingler it's just too slow to hang imo. I'd like to see more high-level players experiment with it, and I can see it moving up/down for me with more games to reference, but mid C seems fair for now.
Dragonair
It's very underwhelming in PU, but it technically has a niche. It can spread para and chip away at stuff with wrap, but even when APT wasn't transitively banned here, Dragonair wasn't eating much at all. Now that it's relegated to purely parawrap, it's starving.
Poliwag
It's technically the fastest sleeper in the tier, and can be used in cheesy ways to exploit Nidoking/Golduck as a result, but it's fucking Poliwag. This thing is in danger of dropping to SU, and even with an amnesia up it's still not hitting very hard. 40% of the time it's going to do nothing and then die, and the other 60% it's going to do mostly nothing and then die. Like Kingler/Sandslash, this thing was brought to 0/82 PUBD games, and unlike them, with Poliwag I completely understand why.
Nidoqueen
Wow, how the mighty have fallen. With Nidoking in the tier, there's genuinely more of a reason to use Poliwag than there is to use Nidoqueen. King/queen don't work well on a team together, and king hits better damage thresholds and more importantly has a better speed tier. If you're ever thinking about bringing Nidoqueen as a diet 2nd Nidoking, consider bringing Pinsir/Machamp instead. They at least fill different niches and have different entry points, rather than a strictly worse copy of a mon you already have.
D TIER — Bro thinks he's on the team
Arbok
Worse Dragonair. *Maybe* you could have a reason to bring this on some kind of weird paraspam/wrapspam team?
Muk
I love the stupid sludge pile, but it can't hang here. Throwing it out loses you so much tempo, as it doesn't hit very hard and lets your opponent switch into something that does. You could maybe try to catch something with a stray boom while preserving your own valuable pieces, but you better hope they don't have a Gastly/Graveler.
Slowpoke
This meta hits way too hard for Slowpoke to find a home here. It can't restloop without either dying or letting a mon set up, and it doesn't hit hard at all, even with an amnesia up. The best it'll do is spread a bit of para and then either die or sabotage your game through inaction.
These Chumps
They're all ass. They're strictly worse versions of mons higher on the list, but I've seen competent-seeming players try to make all of them work on ladder. None of them can hang in PU, and the opportunity cost of bringing them is unjustifiable imo. Unsurprisingly, despite what anyone might confidently assert early into current PU, Flareon is NOT in fact better than Magmar.
was in the tier.
[confused ray]
