DPS whacking on the boss behind the boss means tanks have to move around collecting adds. Extra healing pressure with DPS who can't avoid AOE or who are so trigger happy they just have to put AOE on the adds (hey look at my meter I top the charts!) Extra healing means extra enmity so tanks have to spend extra resources maintaining aggro...
You talk as though anything in this fight hurts, healing pressure? what healing pressure?
As a melee DPS you just stay under Vishap, ranged can be underneath or way off to the side, doesn't matter. Do the fight like I described and you'll kill him before the 3rd Dragonkiller is in range.