The post-game is minimal. There’s Mewtwo, there are some roaming legendary birds, there’s Zygarde, and there’s a single town with the worst Safari Zone ever, the worst Battle Tower-type place ever, and a couple of extremely tiny story beats. There could be some other things to find, but, at best, this is nowhere near what the last two generations have offered. Compared to other Pokémon games, saying that this one is stuffed with content is nothing if not laughable. It’s like Ruby and Sapphire but without the sense of discovery (or the charming personality).
There are around 70 new Pokémon to find and most of them aren’t that great. I would not mind the low count so much if the designs were so much better than in previous generations, but they’re substantially worse in my opinion. I know it’s subjective whether the low Pokémon count is a good or bad thing, but I play new Pokémon titles for new creatures just as much as I do for new gameplay, and the low count terribly disappoints me. Furthermore, they revealed around half of the new guys before the games even came out, which is a messed up method of advertising which spoils one of the biggest points of the game before anyone even touched it.