Well, Now the other suggestions outside that around S tier, with a mostly green tone apparently.
Kleavor from A to A-. This is a no brainer, Kleavor just isn't fast nor bulky enough to work consistently, and I've noticed it doesn't get as many OHKOs as it would like, nor 85 speed works to make it a consistent scarfer. Is only a lead and even then it feels outclassed at times by Stealth rock Arcanine or U-turn Scizor. Don't get me wrong, Stone axe is amazing, is just that Kleavor is not that impactful at top level.
Galarian Zapdos from A to A+. This pokémon is just ridiculously hard to beat without trading because nothing bulky resist flying + fighting. Has survivability issues and is prediction-reliant, but trading 2 for 1 is just worth it on almost any scenario.
Breloom from A- to A. You know the deal by now, a frail, somewhat slow wallbreaker with technician, mach punch and spore. Those tools are as useful as ever, maybe even more so than before due to no longer having to compete with King? Queen? Meowscarada. It has the same issue of either having the chance of surviving hits or guaranteeing Bullet seed's damage, but being a fighting type no flying type wants to switch into due to rock tomb and a grass type no fire type wants to switch into makes it just a surprisingly good mon at its job.
Hippowdon from A- to B+. The meta is just unkind to this creature. Lots of earthquake immunities, lots of boots, lack of rapid spin unlike some other ground types and is a bad tera user, not to mention sandstorm kinda limits your teambuilding significantly. Despite having recovery it is somehow mostly outclassed by Donphan and Iron Threads due to how balance became less relevant lately.
Rillaboom from B+ to A-. Grassy terrain is just amazing utility against the Donphans, as is knock off, U-turn and being the only viable user of the valuable leech seed. Now that Meowscarada isn't there and there's lots of targets who just get destroyed by wood hammer's 234 Base power, the grass monke finds a good niche to be a good UU pokémon worthy of the A tier.
Slowbro from B+ to B-. Slowbro has it rough on the higher levels, really rough.
Issue 1: Slowking outclasses it in the bulky psychic department almost entirely due to chilly reception.
Issue 2: Quaquaval and Gastrodon. As a bulky water type Quaquaval matches better against the current meta due to actually checking Arcanine, Kleavor, Hydreigon and Skeledirge, while Gastrodon with its electric immunity against thundurus and hazard setting capabilities are also a problem.
Issue 3: Volcanion has a better attacking typing and steam eruption, a move no one wants to switch into.
Issue 4: Galarian Slowking is a better setup sweeper due to sludge bomb + flamethrower and not being weak to U-Turn or electric. All in all, there's not a lot of reason to use Slowbro in UU outside checking Quaquaval and Zapdos somewhat better than Slowking.
Chesnaught from B to B+/A-. Spikes + leech seed + spike shield is a set a lot of pokémon don't have a reliable answer to. The passive chip damage while not being passive itself due to Wood Hammer or Body Press. It has only one trick and falls against special attackers in general, but is quite a good one at its role, although I'm not sure if it deserves A- or just B+. Many have mention its talents and I have to agree with them.
Magnezone from B to B-. Trapping steel types had become increasingly unreliable after the addition of iron treads, while the prevalence of Hisuan Goodra and Scizor as steel types it cannot reliably trap and tera being a thing means is just not very good at its job. To put salt in the wound it needs tera itself to trap most steel types which makes its applications quite niche.
Pawmot from B to B-. Pawmot is struggling right now to find a place. It's just incredibly difficult to justify your usage when Galarian Zapdos and Thundurus-Therian, who have more power and either bulk or utility, and the speed advantage isn't that relevant considering Iron treads exists. Does that mean the pokémon has no niche? Not really, because it has the tools to be an effective hybrid of revenger killer and offensive support between Ice punch/Seed Bomb, Double Shock, Close Combat, Revival Blessings and 105 speed, as well as cheeky tactics like nuzzle or encore, is just that it struggles to find usage in most teams.
Aqua Tauros from B to B-. Is in the same realm as Pawmot. Is a mon I know personally due to usage and I know its niche; is a water type for balance teams who can reliably check Arcanine due to higher speed and psychical bulk, while also being an assurance against screens and a danger due to bulk up. Is useful but outside of that it's outclassed by Quaquaval's aqua step. Is also oftentimes just investing to outspeed Breloom, to the point I wonder if it's even worth using it over a speedy Quaquaval who is stronger and can outspeed Breloom anyways. Bulk is useful but not enough to justify using it over better fighting types most of the time considering is outclassed in other areas.
Wo-Chien from B to C+. Outside live reactions, What is this thing exactly doing in UU? Yes, it has Knock off, but so does Tinkaton, the two donphans, Muk, Cyclizar and Rillaboom, each one having a valuable niche as well to be used over Wo-Chien like fairy/steel type, rapid spin, Toxic or u-turn. Leech seed is great, but also something Rillaboom offers while having better recovery and offensive pressence due to grassy terrain. It has great defensive stats but that isn't gonna help you against the many powerful wallbreakers and setup sweepers without offensive pressense or more reliable recovery, specially with that tera reliance due to how bad dark/grass is on defense, and Zarude existing makes things just harder for the snail being in your team outside stall who is fading btw. Speaking of Zarude...
Zarude from B- to B+. This pokémon is just a menace. After the tier lost Meowscarada and Greninja, this is now the fastest dark and grass type around, with a moveset you just can't predict. While in the previous UU it was mostly an offensive pivot, nowadays the way to go seems to be setup sweeper thanks to the new access to swords dance and trailblaze, while it still has the old tricks under its sleeves like fast U-Turn, jungle healing, bulk up and taunt to setup more reliably or pivot. Just a good pokémon if you need a dark type who outspeeds Thundurus-T and has grass/fighting coverage, although its several weaknesses keep it in check and outside A rank for now. Again, another pokémon mentioned quite a lot that I agree with.
Sadly I have not a lot of Info about the C tier due to how niche they are and therefore not knowing how they perform in battle.
And finally, the most important things...
- You should update the showdown link to go here instead of the old VR.
- I think a Quaquaval vs Skeledirge art would fit here the best. They have a clear rivalry due to being paldean starters and are also some of the best UU pokémon around. That alongside a Donphan vs Iron Threads could fit here amazingly for obvious reasons. Maybe in some sort of Battle royal motiff with each one facing the otter other, or maybe putting them in a double battle portrait like the XY anime when a mayor battle started, with Skeledirge&Iron Treads (New) vs Quaquaval&Donphan (Old).
PS: Now I have a better image of the C tier so I can make suggestions from there. Also some minor editing.
Mimikyu from B to C+. Another pokémon who just struggles to find a role. Is slower than Hydreigon and Zapdos, is quite weak and it relies a lot on disguise to work, and even at +2 it isn't OHKOing that much considering Shadow claw fails to 2HKO Hisuan Arcanine. The only thing it's good at is checking stall for HO teams, and even then they're likely to pack Skeledirge precisely for pokémon like Mimikyu. At least is better at spinblocking than Zoroark and Gengar due to disguise.
Bellibolt from C+ to C. The pokémon just is completely unremarkable. It's trying to be a defensive electric type with slack off and parabolic charge with muddy water and volt switch to pivot and hit ground, which is neat but not very practical when the tier just check it naturally due to how passive it is outside the charged moves and how good grass types are atm, while being slower than Donphan alongside weak to its earthquake is just a recipee for disaster. There's a reason it had 0 usage in the last tournament, and I would be tempted to say outright unranked if it wasn't due to Quaquaval and Tornadus-T existing.
Brambleghast from C to C+. This pokémon has an oddly good niche when looking with a keen eye. This pokémon is both a spinner, a spike setter and a spinblocker who can actually beat most spinners unlike most ghost types, and has a very useful Hurricane immunity against the popular Tornadus-T, as well as arguably the best recovery move in strenght sap. Yeah, it fears Ice spinner and strong knock offs and is not precisely strong at all, but its utility talents are quite useful for semi-stall teams to not lose to the evil lego pieces after having to sponge multiple knock offs.
Rotom-Heat from C to C+. The niche of Rotom-Heat is small but worth mentioning. Is mostly a fire type who scares slower water types and an electric type who can switch against grass, ice and ground moves due to better bulk. Is quite specific but it sees some tournament sucess because some balance and volturn teams do appreciate their fire type to pivot with volt switch and being able to check Tornadus-T and some water types. It needs further testing to move up from C rank though.
Rotom-Mow from C to unranked. The tier has lots of high quality grass types, many of which have u-turn. The tier also has Thundurus-T as an electric type. Finally, lots of fire types who destroy most grass types. What I'm going to is that every niche I can think off for Rotom-Mow it gets outclassed at. Why do I want my electric type to be outsped by Arcanine and Zapdos? Why do I want a grass/electric when grass is already good against water and ground, specially one who cannot really spam its grass STAB? Why do I want a nasty plot sweeper who gets destroyed by the most common unaware mon in the tier? Even the few niche things it has going for are performed better by Rotom-Heat and Hisuan ELECTRODE. I just see nothing other can't do better, therefore is not a mon worth rating.