In a lot of player's eyes, it seems to be Experience Share is what made the recently-released Pokémon games (XY and ORAS) look easy.
In previous games, Experience Share had only allowed us to pass off battling experience we earned only towards one Pokémon (whichever was holding it). This time, however, it's much, much more different; instead of one, they're shared among each and every team member, and on top of this, all exp we gain are more high in number. Personally, I like it (as it saves a lot of time on training), but there are others who don't. For those who do dislike, their options are to either keep it enabled, or disable it completely.
Though, I believe it would be nice if they were to update this system and make it so that we are permitted to turn off the feature on select Pokémon rather than all, I feel it would go a long way as far as difficult is concerned (after all, higher our Pokémon's levels are, the more easy we'd find NPCs to be to have matches against). Generally, it'd be satisfying a lot more people than it is now, I feel.