I wouldn't mind it so much as an accessibility feature, but in my playthrough of Pokemon X way back when, it was a bit too easy, and it got boring towards the end (except for the Elite Four). I also had a Mightyena on my team, and I could not get it to where the rest of my team no matter what I did. Every time Mightyena went up a level, the rest of the party would too, so it was a losing game, and I ended up not using it. "Should I have been using a Mightyena on my team?" No, but kids are going to be playing these games with sub-optimal teams for various reasons.
The amount of "Group Think" required to tell people to just box their starter to keep it from overleveling is quite astonishing. Again, I'm fine with whoever needs the modern EXP Share having it, but it'd be nice to have it toggled off.
(Before I bring up this next point, no, I haven't played that many modern RPGs. I'm trying to catch up with action adventure games and old-school RPGs like Earthbound.) I don't really know about this "All RPGs already moved onto leveling up the whole party" thing because Pokemon is in such a weird spot. Most of the singleplayer is 1 vs 1 and a big game of rock-paper-scissors at that, and you can capture nearly every playable monster in the game. Are other modern RPGs comparable to this?