In my opinion they are hard ,but in the wrong way. They are hard because of the constant spawn of adds. I would like to see more fight mechanics in the bosses.
From my experience so far: Every dungeon boss in this game has the same pattern ,sadly. They have some basic abilities that your group has to avoid and they spawn adds every now and then. Would be great to see some more mechanics involved. All i see now is zerg. Sure some are hard ,but not because of interesting ecnounter…