Moving goalposts.
I swear.... If UBs are just weird pokemon "from another world" (which lets not mention how many sharks we are jumping here.) then why not just say they are legendary? Their role in the game ends up being the same, so it has no difference. Why go through that unnecessary extra step just to be a hipster and different? It is something made to just "be different" which ends up not being different at all. If we can catch them, we can battle with them and trade with them. At that point they are just pokemon and all the ******** they said and showed is irrelevant.
If they are just pokemon, then Silvally was a waste. "They are just Pokémon. Let's catch them and be done with it." No need to RECREATE ****ING GOD. If they are just pokemon, why is there a special ball? Why take away the strategies you created to catch regular Pokémon? There are so many ifs in this whole convoluted shitstorm that are the UBs and all, if not most of them will not even be a problem if they are just bosses.
ultra beasts start attacking alola for reasons unknown
whoa what the heck are these things, we have no idea, lets denote them as Ultra Beasts
assorted people pose the question: are these pokemon
[many, many encounters later] check out their origin story, pokemon from another world, attacking us for <probably a sympathetic reason>
beat up their leader, extend peace branch, now we can catch them in the post game because game mechanics and bonds and blah blah bla h
also are we really going to pretend that, in-universe, all pokemon are considered equal to the point of saying that "just catch them" is a valid thing because like its a thing
we do, but the rest don't. Otherwise people would probably just catch the tapus any time they just show up, or we wouldn't bother with the grandstanding of awakening the RSE legends but not throw a pokeball. Team Rocket just let Mewtwo alone (or, depending on whose interpretations you follow, were trying to get hte master ball specifically for it) rather than just catch it like you do.
Reshiram & Zekrom seemingly (??) can't be caught other than those they chose
A few of Ghetsis' problems probably could have been solved if he just caught Kyurem and used it that way