Dungeons are a main course of playing battle class in MMO though. That you don't find them to be your thing is personal choise you do, it doesn't mean that the battle classes in general are harder to level. You have limited your available sources of experience by yourself. However since vast majority of the players don't find trouble with them, the experience from roulettes can't be ignored when comparing the sources. It's like, if I was complaning it's too hard to get PvP coins because I really don't find PvP battles comfortable.