Some of my thoughts
The Winners:
Reuniclus:
Reuniclus is probably one of the biggest beneficiaries of these bans as it had something against all 5, especially with Urshifu-Single-Strike.
Greninja and Megagross could wall Reuniclus pretty easily with its Acid Armor sets.
Torn-T would remove Toxic Spikes its teammates would set and prevent automatic Toxics.
Darmanitan-G just hits hard and can U-Turn on Reuniclus.
And of course Urshifu would reliably ignore Acid Armor boosts, hits it super effectively too, and would wall Reuniclus as well.
There are more benefits as well, like how Toxapex has more usability compared to Tapu Fini for bulky Water, something Reuniclus can prey on while not having to worry about Tapu Fini Defogging Toxic Spikes or Misty Terrain being ignored.
Toxapex is also generally pretty good alongside Reuniclus as well. Having Toxic, Toxic Spikes, being a good check to Volcarona and resisting Bug, being able to burn Pokemon with Scald, and can Haze opposing bulky set up sweepers too.
Hazard Controllers:
Hazard Controllers really benefit from their main competition being gone. This applies to most Hazard Controllers (Corviknight’s sprite needs to be smaller. smh), with a few exceptions I’ll say later.
Hazard Controllers also like the removal of such offensive momentum being gone, letting themselves remove/prevent hazards much easier. There isn’t much else to say either but they definitely benefit a lot.
Sand teams (especially Tyranitar):
Sand in general benefits Ash-Greninja’s removal. Being pretty important for Rain teams, and generally just being a huge pain as it hits the Sand Setters pretty hard with Specs Hydro Pump and can ignore Excadrill’s Sand Rush with Water Shuriken.
Tyranitar especially benefits the recent bans since like Reuniclus, it didn’t appreciate those 5 Pokemon either (maybe to a lesser extent however). Being Slow, weak to Hydro Pump, Meteor Mash, Close Combat, Focus Blast, Earthquake, and U-turn, as well as the ease of which Tornadus-T could Defog its Stealth Rock and how Urshifu could switch safely into Tyranitar, July isn’t looking as bad for Short Godzilla.
Weavile:
There were some losses for Weavile. Being a fast Ice type that also hits hard meant that it could prey on Tornadus-T as even it could outspeed Torn, on top of benefitting from Tornadus-T’s defogs. Weavile would also be amazing at revenge killing Urshifu as Banded Low Kick would do a minimum of 90.3%.
Weavile makes up for this with Galarian Darmanitan’s departure as a competing Ice Type, Mega Metagross not being around to tank every single hit and easily KO Weavile with Bullet Punch, and would no longer be revenge killed by Ash-Greninja.
Also like everyone has said, Psychic and Ghost types will be much more common, and Weavile is a huge threat to them with its 125 Speed matching Neutral Nature Dragapult, Knock Off, and Pursuit.
Weavile still has Mega Lopunny to worry about, but that isn’t as much of an issue as before since Mega Lopunny doesn’t have 5 of the most lethal mons to back it up especially Ash-Greninja, making it easier to bring in physical walls.
Weavile also doesn’t really mind some of the other Pokemon that will be more viable like Melmetal as +2 Low Kick does more than 3/4ths even without Life Orb.
Melmetal and Mega Mawile:
Speaking of Melmetal, It’s now not just a niche only found on Defensive teams. Thanks to Mega Metagross being gone, it can’t really be Discount Megagross any more.
Not only that, but Urshifu, Darmanitan-G, and Ash-Greninja could do a ton to Melmetal and outright OHKO it with the right coverage and set. Urshifu and Ash-Greninja especially as they both bypassed Melmetal’s Acid Armor (Wicked Blow (which 2HKOs 244 HP Melmetal) and hitting it Specially).
Mega Mawile also benefits in a similar way. While not often using its own Steel STABs, it prefers not to have its Play Rough or to be ripped in half by those faster threats.
Urshifu Water, Urshifu Rock, and Urshifu Jotaro:
Urshifu-Rapid-Strike
Urshifu’s other form and Urshifu’s “other forms” now don’t have to compete with Urshifu-Single-Strike anymore and the latter 2 won’t be obliterated by Urshifu.
While Rapid Strikes isn’t too happy with Ash-Greninja and Darmanitan-G being gone thanks to its typing and Scarf set (which was underrated even when Urshifu was still around), and Toxapex is more annoying for it than Tapu Fini, it still like Mega Metagross gone and its dark counter part.
Terrakion was actually pretty similar to Urshifu in power, and has its advantages like speed (one that was above the 100 base mark), special bulk, not being walled by Fairies, having Swords Dance, Stealth Rock, and Rock Tomb.
What made Terrakion much worse than Urshifu was Mega Metagross using Terrakion as toilet paper. It outspeeds it, resists Stone Edge, has great Physical Bulk, and its STABs are both Super Effective on it.
Also Terrakion lacks U-Turn and Unseen Fist too, something that allowed Urshifu to use when its checks would switch-in and would prevent scouting issues.
Pangoro is Urshifu-SS, but worse in nearly every way imaginable. Only having Parting Shot, Swords Dance, and better special bulk. But like with Melmetal, being a discount version of what currently is a banned Pokemon shows a lot potential. We all know that Fighting/Dark is pretty good offensively, and Dark in general being good offensively can show Pangoro rising up in the future as a pseudo Urshifu-SS. Choice Band, Close Combat, Darkest Lariat, Gunk Shot, and Parting Shot, you essentially have Urshifu again, but with worse Stats and you don’t bypass protect. You then have the option to use Sword Dance, Knock Off, Mold Breaker Taunt, Scrappy Close Combat, Iron Fist Drain Punch, and Toxic as well.
Other Psychic Types and Ghost types:
The 2 best Dark types are gone, which means these guys have more freedom in switching around. The new bans are especially good for psychic types as Mega Metagross would resist their STABs, and I already talked about Reuniclus, most of the points applying here as well.
The Pex:
Like what everyone else is saying, it’s easier to run the Pex now, without the 5 in the Meta now.
Protean Greninja:
While losing one of its best options is bad for Greninja as a whole, and there is less of a guessing factor to what Greninja will be, Protean Greninja will definitely be seeing far more usage in the future simply because a fast special attacker like Greninja is amazing as always.
It also doesn’t mind as much the Battle Bond ban making it less of a guess to what Greninja will be running since Greninja is already pretty diverse even without its Pseudo Mega, thanks to Protean giving STAB to all its moves and having an amazing movepool.
The Losers:
Mega Lopunny now holds the title of being the best Mega currently, but that’s like saying the current richest human in the world is better off because the former richest man in the world had died.
The duo of Mega Lopunny and Ash Greninja is lost until it gets tested for a drop.
Mega Lopunny doesn’t like the fact that enemies like Hippowdon and Toxapex can be run more often or how Sand Rush Excadrill no longer has to worry about Lopunny’s former partner’s Water Shuriken.
While Lopunny is still amazing, and is the best Mega, it only is so by technicality and it hurt by Ash-Greninja’s departure.
Rain Teams:
First Rillaboom was given a Grass Priority move to bypass Swift Swim, but now Rain has lost one of its best Pokemon in Ash-Greninja AND lost Tornadus-T as well. Two major Pokemon features on Rain teams, as well as Urshifu (Honestly Urshifu-Single-Strike was better on Rain ironically enough as it could be used to beat common Rain checks like Tangrowth and Toxapex).
Tapu Fini:
There is very little reason to use Tapu Fini now. It was primarily used for Greninja and Urshifu over other bulky waters, and now it being gone means Tapu Fini doesn’t have much reason to be used over regular Slowbro and Toxapex besides to Defog.
Skarmory:
This thing can’t catch a break huh? One of the few reasons you would use Skarmory over Corviknight as a Defogger is having a more powerful Body Press, which was useful against Mega Lopunny, Mega Metagross, Darmanitan-G, and Urshifu. Now the latter 3 are banned. At least it still hits Mega Lopunny hard while not taking as much damage back.
Just like Tapu Fini, there isn’t much reason to use Mega Altaria anymore and Semi-Stall won’t be as required as before.
Mega Gyarados:
Mega Gyarados before could use Greninja, Darmanitan, and Urshifu as set up bait and was a decent Mega Metagross check thanks to its typing and regular Gyarados’s Intimidate.
Gyarados does somewhat benefit from a larger amount of Psychic and Ghost types, but finds it harder to do so than before. It’s more of a net loss than a net gain.
Volcarona:
With Megagross and Ash-Greninja gone, Volcarona’s checks are much more prominent, and it could beat all 5 of those banned Pokemon as well with after Quiver Dance as it would speed all 5 of them (including Scarf Darmamitan-G), and would hit them hard too.
It now also has to deal with Toxapex and Heatran, and fears Knock Off a bit more as the best Defogger is gone.
It also doesn’t help that Rock types like Terrakion and Tyranitar, as well as Sand Teams, are much better now.
It even loses with Rain teams being worse now as it could abuse the rain against them with Hurricane and its Flamethrower was still threatening against Ferrothorn in Rain.
Changed but still as viable as before:
Rillaboom:
Rillaboom no longer can prey on Ash-Greninja and Darmanitan-G and more, and Rain is less prominent, but Mega Metagross and Tornadus-T are less problems for Rillaboom as they are banned, and it can still be useful against Sand teams too. Rillaboom also kind of prefers being against Toxapex than Tapu Fini as it got to keep its Terrain boosting its Strong Wood Hammers, but Psychic Terrain will be more common to abuse that Psychic Power and Expanding Force.
Sun Teams:
It’s main competition shifted from Rain to Sand, which is slightly better. It did lose Tornadus-T but plenty of Defoggers still exist and Tornadus-T would have less accurate Hurricanes anyways. And it lost Mega Metagross to prey on as well.
Indifferent and hard to say:
Pretty much everything else that wasn’t mentioned.