Some classes are maybe hard to master...ok why not but for what ? To do a dungeon ? No, they are all easy, the only difficulty is to make big pull. For trial ? Normal difficulty is easy, and extrême can be a bit hard if you are not a hardcore player.
The difficulty is only in the savage. You can clean everything, (except trial ex and savage) using your 1 2 3 combo... You dont need to have a good opener or good rotation to do 99% of the content. You can up lvl max without playing your job