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The problem isn't that exp share exists as a difficulty option. The problem is that the games are balanced around the expectation that you are using EXP Share. This is one of the primary reasons why no trainer in the game has more than two Pokemon. If they had larger parties, you would way out level the game even more than you already do.
If they reintroduced old Exp share, added Exp Share All as a post game reward, and rebalanced the campaign to have more trainer Pokemon to make leveling individual mon's not a grind, then everyone wins.
It's not about people having no self control to turn off exp share, it's about Game Freak designing the game in a shit way because of its existence.