They actually nerfed the experience you earn compared to Gen VI, where it was super easy to level up your Pokemon (My HM slave got to level 40~ while not even using it once). Also, I find this game to be more difficult than the previous gen as well so it balances out with the Exp-Share and the experience earning ratio similar to Gen V. I personally keep it on but if you don't like it you can turn it off by selecting it from your bag.