Gonna give a couple of explanations to the tier changes, nothing too in depth but enough to give you all an idea of what's happening!

The sole S rank, everything seems to have moved strategically to allow it to be the best. Less Dragon resists are around and the Ghost resists of the metagame can often crumble to Choice Specs Shadow Ball, especially since it can get a lucky drop and turn the tide of the battle immediately. Its great speed tier also allow it to U-turn out of anything that isn't named Zeraora nor holds a Choice Scarf and the Heavy-Duty Boots set can Thunder Wave or Will-O-Wisp its usual answers to put them in Hex range. The new king sits alone at the tippy-top of the CAP metagame's food chain.
Rises:
A-→A+
B+→
A
Both of these Pokemon saw a ton of usage in World Cup recently, so it's only natural that CAP would follow in using them. CAP has always had Tomohawk keeping physical attackers through either Intimidate or the PranksterHaze set. Both Weavile and Urshifu-R have the tools necessary to circumvent both versions of Tomohawk-albeit they hate taking Rocky Helmet chip from their multi-hit moves

. They also both can run Choice Band sets as well as set up sets and each set demands a different type of respect. Weavile's coverage is nigh impossible to switch into safely, nailing the Psychic-types that are gaining traction as well as the defensive Flying-types that are always good like Zapdos and Tornadus-T. It can also revenge kill some of the best sweepers in the tier in Garchomp and Dragapult with its Ice Shard as well as Choice Scarf Jumbao! Urshifu-R on the other hand works quite similarly to its Dark-type brother banished to Ubers, abusing Future Sight as it throws massive hits that barely have any switchins.
A-→A
Toxapex is actually perfect for the metagame we currently have; it can beat the two aforementioned breakers, can be a counter to Scarf Jumbao and a situational check to something like Dragapult, checking it if it doesn't click Draco Meteor and even threatening to cripple it with Knock Off. It can also run Shed Shell to escape Heatran's Magma Storm and give you a safe switch to your breakers! Its utility movepool is larger than life itself, providing Toxic (Spikes), Haze for setup sweepers, Knock Off removing items, Scald spreading burns and occasionally even being able to run Light Screen to limit the damage the delayed moves are gonna deal to your other Pokemon.
B+→A-
Just like its Kantonian brother, Slowking-Galar is here to set up powerful Future Sight and then enable your physical breakers-namely Urshifu-R as mentioned above. It also is able to deal with Kyurem, a threat that has been slowly rising in popularity for months now and can take Heatran even better than its Kanto variant by Earthquaking it for a clean 2HKO. It can also take on Tapu Koko and Fini, two Pokemon I think are criminally underrated at this moment. Not only that, it's a fat Pokemon that can self-set to beat Chromera with Future Sight setup>Sludge Bomb>FS landing. Overall a fantastic pick for any team that also frees you to run a different bulky water such as Slowbro or Arghonaut.
A-→A
A bit of a controversial figure, Volcarona has always been seen as "the match up moth" by trying to fish for a good match up and winning in builder rather than in the game. With Heatran and Urshifu-R rising in popularity, its spot in the Viability Rankings might leave some players scratching their heads. Make no mistake, however, as Volcarona teams take those into consideration by trying to overwhelm these exact checks. Volcarona inherently is added to Hyper Offense team, meaning Heatran is always under pressure to switch in and commonly other special attackers such as Geomancy Necturna draw its attention and leave it weakened so that Volcarona can break through it at a later point. In a very similar vein, Volcarona can play the chances game with Urshifu-R, as bulky sets are not OHKOed by its Aqua Jet while standard spreads also hold onto a respectable chance of surviving the super effective priority move. Volcarona can also set up at a later point when Urshifu is invited in, as it is forced to Aqua Jet or risking losing the game, giving you a very clean switch-in to something that resists its Water-type priority.
from the depths of UR:
UR→B
Buzzwole is so good at the moment, being able to just blanket wall a lot of the fast physical wallbreakers in the metagame. Need a Garchomp answer? Buzzwole gotchu. Zeraora is giving your team trouble? Buzzwole to the rescue. Knock Off spam keeping you up at night? Buzzwole doesn't need passive recovery anyway, it forces the game to progress with its muscles. Ice Punch for the Ground-types, Poison Jab for the Fairies, Earthquake or Close Combat for Heatran, Leech Life to suck up Slowtwin HP; Buzzwole can be tailored to your needs. It is undoubtedly weak to Future Sight and hazards + pivoting, but we're not trying to reinvent the wheel here, now, are we?
UR→
B-
Ghost resists have come to mean just Dragapult and/or Pajantom answers in bulky Fairy-types and Corviknight respectively. But what if there was a fast, strong Ghost-type that could beat both of those with its other STAB? Enter: Pagliacci. with a base 151 Special Attack that only grows larger with every kill it gets and a very respectable Base 107 Speed, the clown is here to force you to run a Tyranitar or a priority attacker that can OHKO it or re-evaluate everything you thought you knew about the metagame. Now, Blacephalon is very reliant on proper prediction and a misstep can be fatal for either player but it's definitely got a spot in the meta.
UR→
B-
Mew is as versatile as ever, being able to set up Spikes, delete items with Knock Off and also punish most hazard removers with Will-O-Wisp, run a set with Cosmic Power and Stored Power or Body Press to turn into a unique set up sweeper, or even be used as a suicide lead. Mew can simply fit on many different builds and thus earns a spot on the VR.
UR→
B-
Jello boi can either set up some of the most powerful Future Sights in the tier, or use a physically defensive set with CM and Psychic/Fighting coverage to blow past common special walls. The Psychic-types that act as special walls in the tier like the Slowkings cannot actually do any damage to it and thus have to just pivot aimlessly around it while it sets up in their face. It's a genuinely terrifying Pokemon to face if you don't have the tools to punish it.
UR→
B-
Tapu Bulu functions pretty similarly to Rillaboom, but has a couple of distinct differences. For one, it can't pivot with U-turn or revenge kill with a priority Grassy Glide. In exchange, it gains more longevity with Synthesis and more importantly: better coverage options. Between Close Combat and Stone Edge, the Fire-,Steel- and Flying-types that wanna resist its Wood Hammer are immediately turned into food for this absolute behemoth. Zapdos and Chromera usually decide to creep for Adamant Rillaboom and thus hit 270 Speed. Jolly Tapu Bulu hits a magical 273, being able to creep past those who even try to creep them and land a powerful Stone Edge to send them home.
Drops:
S→S-
Rabia's first born son falls in the Viability Ranking while Mewbby and Lasen are both leading the discussion? What blasphemy is this?! To quote Rabia, the metagame shifts both favor and hurt the ChainChomp. Clefable and friends forcing to take a most specially defensive route while Tomohawk and Equilibra falling off (will talk about these two soon) and Poison-types rising all make Life Orb Garchomp rub its hands as it sees even more opportunities to take over the game. On the other hand, Scarf Jumbao is faster and can revenge kill it with ease, while the rise of revenge killers that use priority to deal with their targets such as Urshifu-R, Weavile, and Syclant definitely hurt a lot. Also, Landorus-T is seeing more and more usage as the Electrics of the metagame demand more Ground-types to block their STAB. Make no mistake, though; Garchomp is one good metagame shift away from regaining its spot as #1.
S→S-
Slowking looks at the metagame and sees more Knock Off and Electric-types than ever. It's by no means a fan. Its most definitely still the best Future Sight setter, having the capability to enable breakers like it's nobody's business while it gives them an absolutely free switch in with Teleport, but it's definitely seen brighter days. Hell, even the things it's supposed to be able to take on such as Urshifu-R, a Pokemon whose STAB combination it resists, it just gets blown back from the Choice Band set while the Pads set can Thunderpunch it for a huge chunk.
A+→A
The afomentioned Ice-types rising means Zapdos isn't a fan. While it does keep a lot of contact attackers in check through Static, it's moreso an overdue drop from Garchomp absolutely demolishing it. Regardless, it still can punish the Knock Off and U-turn spam a lot of players mindlessly default to even if it doesn't like losing its item.
A+→A-
Another long overdue drop, while Equilibra provides a lot to a team in 3 immunities and the Doom Desire that terrorized the later part of USM, it can neither check Ice-types like other Steel-types can nor can it take on the most common Electric-types due to being weak to Zeraora's Close Combat and Krilowatt's Surf. It also frequently has to do way too much for its team, leaving it to get overwhelmed quite easily. Its Rapid Spin is contested by a lot of the Defoggers in the tier as well as Colossoil, another Ground-type spinner.
A→A-
Honestly, the MOST overdue drop of all time. If there is one Pokemon that gets overwhelmed in the current metagame, it's Tomohawk. Loses to other Flying-types, common physical attackers can break it, special offensive threats like Dragapult can switch into its attacking moves and immediately threaten it... It's just not the same as it used to be. It used to be the best Rillaboom answer but it would get Knocked Off and then be a sitting duck for all other physical attackers, not to mention other Pokemon like Zapdos rising to the occasion while doing more. What's that, Future Sight is rising up again? Keep it low.
A-→B+
It's that time of year where there's been a long enough period between team tournaments and Astrolotl being nerfed that it's fallen off the face of the Earth. Quite frankly, the rise of the Ground-types has made it hard to do what it used to, which is be a bulky Regenerator pivot that sets up Spikes. It no longer has Knock Off nor Wish, so its utility is at an all-time low. Will CAPPL make it rise again? My bet is on a yes. But for now, the Axolotl remains low.
A-→B+
Another do-nothing mon falling off? Color me surprised. While Mandibuzz can check Dragapult and Garchomp, if it gets Knocked Off, something it might need to do considering it resists the move, it quickly gets overwhelmed by Stealth Rock. As with other Flying-types, the rise of Weavile threatens it greatly and so it's fallen off. Being a Ghost-type answer that falters to common coverage moves they run such as Thunderbolt or Draco from Choice Specs Dragapult doesn't help its case, either.
B+-→B
Sand as a playstyle is weaker than usual, with the rise of Ground-type usage, Fighting-type coverage and breakers like the Water Bear means Tyranitar is hard pressed to be added to a team. Still, its amazing coverage options means it always can fulfill some role for a team if need be.
B+-→B-
I'm sorry quziel, but your child failed the vibe check. Chromera started out very promising, but people got smart and found out ways to take advantage of it (read: Toxic it when it's no longer a Poison-type). Its role as a stallbreaker is actually performed better by Tapu Fini, another CM special breaker but one that has a better typing and cannot get statused. Is it awful? No. Did we have new toy syndrome for a bit? Definitely, and it's wearing off on us.
B-→B-
Quite simply, other Slows are better. Slowbro relying on checking physical attackers leave it fulfilling a niche that other Water-types like Aghonaut and Tapu Fini strictly do better while also not being...well, Slowking.
B-→B-
Tangy boy has had a rough month, in CAP, OU and Ubers alike, dropping in all of those tiers' VR. Tangrowth is pressured by both Volt Switch due to its awful Special Defense and U-turn because it's weak to, leaving it playing second fiddle to other physical walls. In any case, I think it's not used as much as it could considering Ground-types are seeing a resurgence and Regenerator is a busted ability.
C→UR
We found better ways to pressure Rillaboom so the original KFC recipe is simply outclassed. RIP!
C→UR
Z-moves aren't cool grandpa, go back to retirement you literal fossil.
With all that being said, I can't wait to see how CAPPL is gonna make the metagame evolve. Hope to see something crazy rise
and expect Arctozolt to be at least B+ by the end of it.