I think the difficulty is, to some extent, up to you. Keep your Pokémon in low level, and you're up to a challenge. Grind and make then high, and you better get ready to eat cake.
On the other hand, we have got the tools to grind and make it easy for us this time around, as opposed to earlier games, where you didn't have that many options for grinding, and were left with a big challenge.
In other words, I think GameFreak, imo, made it easier to grind and thus easier for us to eliminate the challenge. If you want a challenge, then you actually have to make decisions and be aware of the difficulty thing, while earlier you didn't have to be that aware of it, since it kinda was hard on default.
I found the game to be challenging and enjoyable, maybe because I tried to make my team have the same levels, as opposed to having one with high level and the rest still around lv 20 XD