I honestly get very tired of seeing threads and people complain about the lack of post game, and I have the same thoughts you do. Battle Mansion is good post game. You have the friend safari, hordes to hunt for even more hidden ability pokemon. You have the whole revamped online content which is outstanding. Looker Missions, filling out your dex which isn't as difficult anymore at all. Legendary Mons to hunt down and capture. Going back and getting TMs you might have missed. I mean seriously people there's a lot to do after the main game is complete. Sorry it's not your standard "Go get badges." sort of thing, but the post game is there. A lot of people don't want to do something that's not presented to them in a way that makes them jump for joy. Talk about difficulty? Battle Mansion is a prime example of difficult battles. These people complain about the game's short sights but they don't seem to appreciate the fact that the whole game is in 3D now. Battles are like stadium and pretty damn cool rather than watching sprites shoot beams at each other. Pokemon it's self has evolved and drawn in even more fans, but the thing about fans is you'll never please some of them. People complained about too many Legends, and now in this gen people complain about the lack of Legends like clockwork. People complain about them adding too many pokemon each generation, so they added less and focused more on graphics, now I see people complain about the lack of new mons this gen.
The funny thing is. We're still solving mysteries within the game! It's rare but there's items we have no idea what they do, NPCs that seemingly have no purpose for now and a lot of other unexplained stuff. That's rare in a game made in this day and age, folks. I'll say honestly the only thing I was kinda sad about was where you find Mewtwo. I expected a whole cave area to explore like Red & Blue with Mewtwo at the end. It's like Mewtwo wandered up, gave some random guy 20 PokeDollars to stand guard in front of the door, and wait for a trainer. It felt weird, other than that though it's all good I feel.