I've never minded new Pokémon being exclusive to the post-game. It didn't bug me in Gen II, it didn't bug me in FRLG, it didn't bug me in BW (the reverse situation actually), and it didn't bug me in Gen IV. It's fine and I like being able to have meaningful encounters that can only be found post-game, it makes it more worthwhile. There are some people who are absolutely livid about this, probably the same people who think the dex cut is the worst thing about SwSh.