Rises
Bellossom A+ to S
I think it's no contest. Bellossom is easily the most splashable Pokemon in the tier. It's able to check a large majority of special attackers like Wailord, Plusle, Pikachu, and Haunter while also being really difficult to switch into due to Stun Spore and Sleep Powder creating a 50/50 dynamic of whether you can switch your bird into it and not be completely ruined or switch a slower Pokemon but instead they are out of commission due to sleep. It's contender for the best Pokemon in the tier, and feels like it's only not seen when the team needs a Grass-type spiker.
Dewgong A- to A+
Dewgong is definitely on par with Wailord in this metagame. Its notably faster so it can check Flareon much better and the Ice-STAB is more important lately when Bellossom is quite popular. It also has more utility options than Wailord does in Encore, which can shut down Substitute Pokemon like Pelipper or setup Pokemon like Calm Mind Sableye and Chimecho. It's not better than Wailord since Wailord resists Steel, making it a better Metang switch-in and also is not weak to Fighting, making it better into Hitmonchan. But, I would say that Dewgong's positives and just as good, if not better, than Wailords.
Pidgeot B+ to A-/A
I think Pidgeot is the worst bird, but the worst bird is still a very good bird. Notably, out of the two, It feels like Pidgeot's typing leaves worse defensively despite good bulk. Murkrow can always check Chimecho, Golbat is a great Hitmonchan answer. Instead, Pidgeot can pivot into some moves like Earthquake/Hidden Power Ghost on Hitmonchan, or take a hit from Chimecho as well and switch-in. It just doesn't appreciate the damage because it already takes a lot of recoil from Double Edge. Offensively, Pidgeot has a lot more going for it. Normal-type moves are quite spammable and hit hard with high base power. It also has priority Quick Attack which is much stronger than Golbat's Quick Attack due to STAB. This still keeps it relevant and probably goo enough to be in one of these tiers.
Pikachu B+ to A-
Pikachu's firepower is more important in a metagame where things just got bulkier. Sure, Bellossom isn't a great development for Pikachu, but everything else is pretty good for Pikachu, so its a no brainer it rises.
Roselia B to B+
Roselia still feels like it sucks a lot of the time but one big improvement in this metagame is that it is by far the best switch-in to Bellossom and gets free Spikes versus it. It can still kind of check Electric-types and Water-types, but this is the main thing. It only fits on fat teams but on those teams, Roselia has its niche, and a pretty decent one at that.
Murkrow B- to A/A+
Murkrow has had a really great glow up in this metagame. Out of all the birds, Drill Peck on Murkrow is by far the most spammable move it can run. No immunities, is a pretty high base power move, and hits a good few Pokemon in the tier. It hits the hardest with its coverage additionally as it has the highest attack stat, and it's Dark-typing gives it defensive utility against Chimecho despite not having great defenses. Out of all the birds, I also think it is the best one when not using Choice Band due to some utility it has in its movepool in Thunder Wave. Overall, while not the most splashable, it can definitely be one of the more lethal birds.
Mawile B- to B/B+
Mawile has gotten better for reasons said before. It is a great bird answer and Baton Pass pivotting is more important lately. Some combos I have really liked with Mawile is pivotting into the birds, pivotting into Pikachu, and pivotting into trappers. I think thats all it really needs to do to rise, bird answers are way more in demand.
Diglett B- to B
I think Diglett's niche has become more in demand. It still does everything it did before but has competition in Trapinch. They do different things though, since Diglett and outrun Pokemon like Flareon and remove them, can outrun Pikachu and remove them, and a lot of the other Pokemon named below can also be removed. Sometimes it can remove Grass-types if you get it in on about a half hp Bellossom or get it in on Cacturne or Roselia as well. Diglett does needs support/great pivotting to get in whereas Trapinch usually can work by itself, but I think Diglett has a higher skill ceiling. I think its enough to rise.
Trapinch C to B
Trapinch has some notable traits over Diglett. Physically Defensive Trapinch can switch into and trap Metang, and also trap and remove Sableye who do not run Rest. It can also trap Arbok and other Poison-types on switch as well. In a metagame where birds are doing great, I think being able to remove the most common bird answer in the tier and some other Pokemon additionally on top is a great niche to have.
Shuckle C to B-
Stall feels like it got better. Shuckle is good on stall. That it, not really much else going on with Shuckle.
Pineco UR to B/B+
Pineco spikes on quite a lot of Pokemon. Notably, Hitmonchan, Metang, and sometimes Bellossom. Sometimes, teams really want a little insurance against these Pokemon, and Pineco offers them this and also offers Spikes. It's move pool is quite nice too, has Earthquake so Pokemon like Pikachu and Flareon do actually have to be careful switching in, and can also trade using Explosion. All round pretty good Pokemon.
Omanyte UR to B-
I think people underrate it. Every team needs a slot for birds. Omanyte can do this well. You can say that Omanyte spikes on Pidgeot but its not the truth. It spikes on every single bird. The birds are really good, so Omanyte will always have a niche in this metagame. A lot of top mons in this metagame appreciate Spikes, such as the birds and also Haunter, so the demand is also definitely there to have these spikers, and as an option, Omanyte is definitely appreciated as the role compression lets your build go more offensive.
Shedinja UR to B-
Shedinja is real. This Pokemon can be singlehandly one of the most scary Pokemon to deal with in the tier. Wonder Guard completely blanks a good majority of the metagame, such as Water-types, excluding Octillery, Electric-types, Offensive Metang, Haunter who are not running Will O Wisp/Hidden Power Fire, and etc. It's best matchup will be versus teams who ditch Spikes entirely, usually for trappers like Trapinch or Diglett. It's worst matchups are fat spikes teams with Sableye. However, just seeing spikes isn't an autoloss matchup for Shedinja, since I would advise you run a Rapid Spin Hitmonchan with it always. Shedinja becomes degenerate with a SubPass Pokemon like Flareon. It's really nasty to pass a Substitute on a Water-type to then see Shedinja come in, and Shedinja under a Substitute does wall more things, such as Toxic Metang, and forces the opposing player to go into a Pokemon who can break Shedinja's Substitute, which means it takes a hit from Shedinja's pretty high attack stat. Niche, but very deadly.
Drops
Metang S to A+
I don't think Metang is good enough that it should be in S tier. Notably, I think it lost its ability to be a great Haunter check in this metagame since the majority run Will O Wisp which ruins Metang. While it can act as your answer to birds, I think this slot is contested more in this recent meta. Mawile is better lately since it takes less damage from the birds and Baton Pass pivotting is more important in this metagame when games are typically slower. Relicanth has proven itself lately as a great bird answer while being pretty offensively threatening. Omanyte has already been discussed. So when we look at what is unique to Metang, it's the MU's against certain special attackers, like Chimecho and Plusle, In my definition of S tier, I don't think thats good enough since Metang's role is not so unique anymore to be a standout Pokemon that an S tier Pokemon should be.
Compare it to people like Bellossom, being by far the best SpDef Grass-type who is able to blanket check a large majority of the tier and has great utility options, Hitmonchan being the only real Fighting-type with great breaking potential and priority Mach Punch, and Haunter, a fast Ghost-type which performs many defensive roles such as checking Hitmonchan as well as offensive roles and has a good amount of set diversity and utility in its movepool. Metang is a good bird answer who also checks some special attackers like Chimecho and Plusle. It doesn't feel the same or unique enough.
Kecleon A to A-
I feel like Kecleon hasn't been as good in this meta. Notably, its got stiff competition from Bellossom as a blanket special wall lately, and while it does have Rest, it doesn't like Haunter running more Will O Wisp, as it forces it to Rest much earlier. Still, it can do a lot of what it did before, such as beating Chimecho, and Dewgong being more popular is good for Kecleon, as it does a lot better into Dewgong than it does into Pokemon like Wailord. Still, I do think it has not been as good lately.
Huntail A to A-
I think Huntail has more problems lately. Notably, Bellossom is quite common and usually sticks around in a game to when Huntail starts popping up. Spikes are also not as easy to set up as they were in Glalie meta, so it does take a bit more effort to get Huntail to clean. It's still pretty good but I think its not as easy to use anymore.
Pelipper A to A-
Despite Hitmonchan getting better, I do feel like Pelipper is worse. Pelipper really liked having Spikes everywhere as not only did it not care about them, but it chipped into all of its checks pretty heavily and when combined with a SubTox set, made everything get chipped down pretty consistently. That isn't nearly as common anymore, so while Pelipper is still good for dealing with Hitmonchan and pretty uniquely shutting down Flareon, it's not as effective as it once was.
Torkoal A to A-
I can't pinpoint exactly why Torkoal feels worse. I guess Water-types are more common, but i just don't think it stacks up to everyone who is in A tier at the moment. Still good though.
Seadra B to B-
Without Spikes, this doesn't feel nearly as effective. On top of that, Bellossom shuts this down quite heavily. It's no where near as good as it was in its prime, but keeps a niche of being a fast Water-type with good power, which is more than a lot of what C tier can say.
Venomoth B to C
I don't have to really explain this. Venomoth sucks, it is only good now as a Sleep lead who can SubPass in exchange for a dead slot after that. If somehow people can use that one trait and make it actual worth something on a team, then I can see it getting a little better, but no way now.