Hey there, Sun teams are in my opinion a bit underrated in the current OU metagame and so I’m glad to see one and I will try to help you improve it to make it as much viable as possible.
Torkoal
Torkoal is indeed a great Sun setter (and even the best). Regarding your move choice, Stealth Rock would be a pretty good move as Torkoal will often be your lead and you want to be able to set up Rocks with it to help your Sun abusers breaking through the opposing team. Yawn isn't really a great choice; it can be replaced by Stealth Rock. And you'd want a physically defensive Torkoal, as it isn't really good enough as a SpD wall, plys the extra defense would help Body Press to hit even harder. Otherwise, all looks fine here. Therefore, here's the set that you can use:
Torkoal @ Heat Rock
Ability: Drought
EVs: 248 HP / 252 Def / 8 SpD
Bold Nature
IVs: 0 Atk
- Rapid Spin
- Body Press
- Lava Plume
- Stealth Rock
Landorus-Therian
Lando-T is a pretty nice Pokémon as it helps against Garchomp and opposing Lando-T, which are big threats to Sun teams. However, I like Corviknight more than Lando-T as it has reliable recovery in Roost, but Lando also works fine, after all it's one of the best Pokémon in Gen 8 OU lmao. I’ll just change the moves a bit; now as we have Stealth Rock on the Torkoal, you don’t need Rocks on Lando too, it can be replaced with Knock Off. And also, specially defensive Lando-T are on the rise now, so you got a SpD wall as well, which can still check Garchomp and all. Lando-T also acts as a pretty cool Heatran switchin, and Heatran’s a big threat to Sun teams, so that’s another plus point. Thus, the new set:
Landorus-Therian @ Leftovers
Ability: Intimidate
EVs: 248 HP / 4 Def / 252 SpD
Careful Nature
IVs: 29 Spe
- Earthquake
- U-Turn
- Defog
- Knock Off
Venusaur
Venusaur is undeniably the best Sun abuser in the game. This is mainly because of two things: Chlorophyll and Growth. Life Orb is a good item choice to strengthen its power and allow it to get kills more easily. Sludge Bomb is also an option as it’s a stupidly strong STAB, but overall Earth Power is preferred as it hits Heatran’s super effectively. I’ll suggest only one change here, though, swap Solar Beam for Giga Drain. Giga Drain is much more helpful than Solar Beam because even if it’s less strong, it gives you an opportunity to heal yourself and potentially overcome Pokemon like Blissey that commonly try to switch-in and stop your setup attempt. Here is the set with that changes:
Venusaur @ Life Orb
Ability: Chlorophyll
EVs: 252 SpA / 4 SpD / 252 Spe
Modest Nature
IVs: 0 Atk
- Growth
- Earth Power
- Giga Drain
- Weather Ball
Charizard
Charizard is a great Sun abuser and can deal massive damage thanks to Solar Power. Air Slash is a pretty weak STAB which doesn’t really hit anything important, Urshifu is dying to Solar Beam anyways. However, there are only two reasonable choices here which are Choice Specs that gives you an amazing wallbreaking power and Heavy-Duty Boots so that you can come easily on the field even when Rocks are up on your side. I’ll propose a version with Choice Specs, but don’t hesitate to use Heavy Duty Boots if you struggle against Rocks. Anyway, here is a set you can use for Charizard:
Charizard @ Choice Specs / Heavy-Duty Boots
Ability: Solar Power
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Weather Ball
- Overheat
- Solar Beam
- Scorching Sands
Heatran
Scarf Heatran is a great option, as it acts as a form of speed control and a full-powered Eruption is almost impossible to switchin to. It also has access to other coverage moves in Solar Beam and Earth Power, which nails opposing Tapu Fini (and Urshifu) and Heatran, respectively. Great set, nothing to change actually.
Victini
Victini is actually great, don’t hesitate to use it. It has an almost impossible to wall V-Create, and access to great coverage moves too. I’ll suggest a Choice Band variant here, as Scarf Heatran is actually enough speed control, plus a Band V-Create isn’t something any Pokémon would like to switchin into! I’ll also change the moves to V-Create as your main fire STAB, Bolt Strike to hit Water types, U-turn to be able to pivot and Trick to annoy defensive Pokemon like Toxapex by giving them a Choice item. The new set with the changes:
Victini @ Choice Band
Ability: Victory Star
EVs: 252 Atk / 4 SpA / 252 Spe
Jolly Nature
- V-create
- Bolt Strike
- U-Turn
- Trick
That’s all for the answer, and here’s the PokéPaste with the changes. Hope it helped!