You know, there's one place I actually struggle trying to DPS with as WHM and that's Dun Scaith, particularly Miss Thirty Souls. I find that people just die to that fight left and right from Shadespin and that one move she does where she charges and launches an AoE, and there's not much I can do to really stop them from dying once the debuffs stack. Having to also manage people not standing still for that one detrimental effect cuts into that as well so I typically just don't even attempt to DPS for that fight anymore.