Here's some scrambled ramblings from me to supplement the new survey.
Reviewing potential issues
Final Gambit / No Retreat
Probably the two biggest issues I can think of in STAB at the moment individually, but I'd particularly like to highlight the combination of using both at once, as I feel like these two get considerably more broken once you pair them with eachother. The ability to just completely get rid of a hard counter for an opponent as well as threaten a sweep by just using No Retreat makes this a particularly insane combination. Not only that, but Urshifu-R isn't even the only user of this tactic - I've tried it out with Keldeo and Kommo-o too, and I figure such a combination is also viable on Buzzwole as well.
As for individually, No Retreat can be seen as a way to just instantly seal an endgame without much hassle. Fissure has done it with Terrakion, I've done it with Buzzwole, FC has pulled off a similar thing with Keldeo, all of which have tended to near instantly end a game even with good revenge killing mechanisms. No Retreat simply makes a mon too bulky to really handle via conventional means, gives them a speed boost enough to outspeed most Choice Scarf users, and the lack of super-effective priority on Fighting-types makes them impossible to handle offensively - you must have a defensive answer to a No Retreat user, or you will lose the game near instantly. Answers to these exist, but outside of Toxapex there isn't really a global answer - and as I've mentioned before, the combination of No Retreat and Final Gambit together can be used to get rid of what few walls you have to a sweep.
Final Gambit is kinda awkward in a metagame with few Ghosts - they can make otherwise weak mons in balance matchups like Keldeo or Buzzwole instantly threatening if they are not needed as speed control. Though this does not necessarily make Final Gambit broken as a singular move, it does significantly increase the viability of many mons that would otherwise suffer with hard answers, like the aforementioned Urshifu-R. The simple potential to lure an important defensive mon with something like Buzzwole (or even Kommo-o, as I've toyed with a bit) is fairly unhealthy as is. As a side-note, it is also worth mentioning that Octolock is legal in STABmons, so the combination of Octolock + Final Gambit can perform a similar role to No Retreat + Final Gambit.
Aerodactyl

Aerodactyl isn't really that big of a deal to me. Not only is it vulnerable to chip damage in multiple forms, despite being able to dodge the main form of chip damage in recoil, it also isn't a CB Weavile-tier nuke that just 2HKOs everything that's in front of it. Adaptations such as increase in Mudsdale, Slowbro and Excadrill usage and the general formation of teams (Seismitoad + Tyranitar, RH Ferrothorn, King's Shield Heatran) all tend to signal that the metagame is moving away from Aerodactyl, and that teams are generally getting better prepared for its breaking antics, even if that is through Regen pivoting + RH half the time. Do try out Adamant LO DD on HO though, the speed of this thing is insane and as a breaker it's not even half bad.
Cinderace

It's become pretty evident throughout OMPL that Cinderace isn't really much of an issue, but given there were some early sparks about it, I'd still like to look into Cinderace, and why, like Aerodactyl, it is finding itself going out of the metagame. The general increase in Toxapex & Mudsdale usage means that Cinderace has to pick its moves a lot more carefully - for example, it often wants Fire Lash for Toxapex and co., but this is beaten by Mudsdale, and Sacred Fire tends to lose to Toxapex. Additionally, the increase in usage of King's Shield in general makes it a lot harder to use as a bulky offense breaker. Pretty good anti-offense mon outside of this though, still worth running
Underrated Pokemon
Heatran

I stumbled upon this mon again during the later half of OMPL just by pure co-incidence. I remembered that a specific Heatran set I used to use (Magma Storm / Earth Power / Doom Desire / King's Shield) actually matched up very well now that Slowking and Rotom-Wash usage were down from the last few weeks, paired it up with an interesting Rotom-C set, and watched it absolutely decimate builds with a slower approach to them. King's Shield also made it so that Heatran was very difficult to approach offensively, as breakers like Aerodactyl, Cinderace and Tyranitar don't really want to attack into a King's Shield. Because of King's Shield + Doom Desire and the chip from Magma Storm, it's also very easy to put Doom Desire into a good position where it will be able to hit the opponent in a bad spot most of the time. In general, I think the synergy of Heatran + Tyranitar is actually REALLY powerful in the current metagame, and I expect to see Heatran rise pretty significantly over the next few weeks.
Later on, I started using Flame Body variants of this mon, and it turned out these were
even better than the Flash Fire variants at punishing physical breakers who wanted to start smacking things right out of the gate. It also helps that Flame Body Heatran can punish Flip Turns, making the residual from Magma + King's Shield even more powerful. Further yet, dropping King's Shield for Taunt or Toxic can make some switchins hilariously easy to punish - in particular, Taunt allows Heatran to get past Teleport as an answer to its stallbreaking shenanigans, and often forces burns via Flame Body as its checks try to escape.
Latios
Scarf Latios is very good speed control at the moment. Lots of HOs just hate dealing with high power Dragon Energy lategame, and if not needed, Latios can still mess around with most balances just via Trick + Lunar Dance / HWish support. Occasionally you can use Specs, particularly if you're working with Doom Desire Heatran, but Scarf is the main reason Latios has started rising to prominence.
Mudsdale / Runerigus

Both of these mons occupy the same slot, because they're pretty similar in how they both interact with the metagame, as defensive Ground-types that both have a particular niche in staving off certain offensive threats. Runerigus is excellent as it is capable of dealing with HO extremely well, making players second guess when they should be setting up, and often times being able to wall all 6 members of a HO due to its access to Spectral Thief. However, its matchup vs bulkier teams can leave more to be desired, outside of blocking Tornadus-T's U-turns. Mudsdale, on the other hand, is a lot better of a defensive threat against more common attackers like LO Tyranitar, Aerodactyl, Cinderace and Excadrill, and as such has seen a greater amount of usage. Additionally, Mudsdale is excellent at setting Spikes, being able to stall out common removal like Tornadus-Therian, and dissuade certain removal like Sylveon.
Zeraora

Zeraora is a very potent form of speed control in this metagame. At least on par with Aerodactyl, better than Cinderace, and has a considerably better matchup as a revenge killer. Even just going with the standard Bulk Up variant, it's pretty easy to batter yourself through common pivots like Seismitoad, Buzzwole and Ferrothorn, and this is a mon that's capable of doing that nearly every game with how easy it is to get in on even something as scary as Tyranitar. The extra power provided by Bolt Strike is also amazing to get past some annoying fatmons like Clefable who pretend to answer the mon, even if it comes at the cost of some reliability. If deemed necessary, Zeraora is also capable of throwing on techs like Grass Knot or Toxic on the final slot, making many of the decent answers to Zeraora like Hippowdon and Mudsdale play a very dangerous pivot game. That being said, there are some niche mons that Zeraora really just can't touch, like Runerigus and Nidoking - so unlike other strong speed control mons like Cinderace and Aerodactyl, this is more of a mon that just takes advantage of the metagame state, rather that being something that has all of its strong elements independent to itself.
Recently, I've been messing around with CB Toxic Zeraora, and in part due to the Mudsdale rise, I've been finding it a highly effective variant right now. Whilst it doesn't exactly
beat Mudsdale and Runerigus, it chips them significantly more if you're able to get the right moves off, and is capable of 2HKOing even the bulkiest Buzzwole after Stealth Rock.
Team Structures
Heatran + Rotom-C Double Trap Bulky Offense (Sample submission)
https://pokepast.es/1496d7d940ee29f1
The goal of this build is to use both Heatran and Rotom-C to force defensive builds into bad positions, which Buzzwole can easily capitalize on. As Heatran's answers tend to be bulky waters in the current metagame, Rotom-C ends up taking advantage of the chip damage that is caused by Doom Desire and Magma Storm to its own advantage by switching into these waters and trapping things itself.
(Alternates:
Lati > Rotom-C)