I think dungeons are fine as it is. I mostly do them with people I know in premades and I like to chat and joke while I do them; "engame" difficult would clash with that. If I want difficulty, I go to Coil and and Primals EX. There are still some mechanics that can catch you by surprise, but they're mostly relaxing and that's why I like about them. If anything, since Primals EX and Coil don't have much storyline, I'd rather they focus more on that.