X and Y, the super beam, I think would've destroyed the world, same with Primal Legendary weather phenomenon, and the Ultra Beasts invading, those are just the ones from the newer games, what else, and how many in total are there?
Well, this is simple understand.
Kanto wouldn’t have been destroyed, because while Team Rocket is a Evil Team, they are more like a criminal organization.
Johto also wouldn’t have been destroyed because again, Team Rocket is a criminal organization.
Hoenn would have been destroyed, because if the player hadn’t awakened Rayquazza, Groudon, awoken by Maxie, and Kyorgre, awoken by Archie, Hoenn would have flooded or turned Hoenn into a empty desert.
Sinnoh would have most certainly been destroyed, because Cyrus thought the world was imperfect and wanted to destroy everything, then create a new world where he was a god. (Yeesh)
Unova is tricky. If it wasn’t for the player, Ghetis would rob the region of it’s Pokémon, and making himself all-powerful. So, it wouldn’t be destroyed. But, because the player ruined his base plan, he decided to freeze (destroy) Unova. However, the player in B2/W2 stopped him once again. So, because of the players, the region was gonna be destroyed, but because of the player, Unova wasn’t destroyed.
Short and sweet, Kalos is just Sinnoh but with Team Flare and Lysander and the Super Beam.
With Alola, you said it yourself. The region would have been destroyed by the Ultra Beasts and Necrozma if it wasn’t for the player.
And finally, Galar would be destroyed because Rose released Eternatus, but because of the player, Eternatus was stopped.
So, the regions that would have been destroyed are
Hope I helped!