@.access:
I had a rotating team of 10 by the end and I can tell you keeping each of them leveled in the old way was not asinine.
Yeah, leveling 10 monsters is fine one at a time.
Leveling 30 or 50 monsters when you're trying out all the new stuff and grabbing old favorites, not so much.
I preferred the old method, it forced you to use things and get attached to them and appreciate when they got new moves and felt more personal. But the group share is more conducive to trying everything. I now go from having a team of 8-10, to trying whatever the heck appeals to me, for at least a little while and usually have two boxes of things I'm trying. new and old, until stuff settles in..
The whole group getting experience isn't the problem. Scaling exp rewards should keep you from overlevelling, so that's not the issue. Again, they had that down perfectly in BW. A level 1 mon getting 5000 exp from a monster, and a level 30 mon getting 5 experience from the exact same enemy worked great. Leveling isn't the issue, its everything else. They put the extra heals and stuff in there, the game is designed around and assuming you'll use it and paces it accordingly.
Putting those things in so you don't just stock up on items and get the exact same result is fine, its QOL. Being able to replace something in your party as soon as you catch something new. No more HM slaves. Those are all GOOD CHANGES to make, they streamline the game and take away things that were basically just irritations for irritation's sake. But those were elements of management and planning and tension that are gone, with nothing to replace them. With that change they need to do something else to compensate. If you're pushing the design and gameflow to encourage using giant teams, and completely destroying the ability to freely explore or sequence break anything, then with those design choices they need to do other things to keep it from being completely hand holdey.
(And even then I never used Z moves or megas in the actual game except to see them)
It's not about it being easy. It's always been easy. It's about it being simplified and smoothed out and removing the character and choice of exploration without anything in trade to make the overall game better.
Maybe that change is start letting you have teams of 8 but consistently giving the enemies full teams instead of just 1 or 2 monsters and more general variety. Or maybe its going in the opposite direction of the narrative lock they're implementing and just freeing it to be open world completely, like any sandbox RPG. Make it more like Zelda, so you can go anywhere from the start and face the gyms in any order. (Obviously there would have to be some mechanic in place to keep you from fighting and catching level 50 monsters immediately,,, the already existing badge mechanic probably covers that some.) Have 18 gyms but only need to beat 8 of them, and they scale based on your badge count. Maybe that change is a soft nuzlocke rule, where if they faint, they need to wait X time before getting back up. Something!
But they can't keep simlifying the game (the go games removing wild battles entirely, and eggs, and abilities) and not replace that with something else.