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Experience share is not the problem with XY's difficulty.
I've played it without it as well, the game is still easy unless the enemies vastly out-level you(which they do around Victory Road). In that case it's the bad type of difficulty and you just have to grind a few levels.
The problem with the difficulty is a combination of multiple factors:
-Exp.Share giving you too much experience.
-Exp.Share allowing you to have a full team of 6 pokemon early on with no drawback. >in other games you probably won't have a full team of 6 until late game, if at all.
-Trainers only having 1 or 2 pokemon, and Gym Leaders having 3. Less than previous games.
>This problem is amplified because of the aforementioned point. Not only do the trainers have less Pokemon, the player now has more.
-Mega Evolution
-Super Training being accessible from the start, allowing you a decent EV spread even in the main game.
-Amie offering further advantages in both battle and Exp gain.
-Easy access to Online features and the boosted Exp that comes with traded Pokemon.
Again, Exp.Share is only one problem with the difficulty in XY. Turning it off helps but it doesn't fix the game.