You need 3 healers and a tank (from my experience, but maybe some people are really awesome and can do it with 2 healers). The 4 remaining slots can be anything really. It's not SE's fault if some raid organizer is misinformed or a jerk and won't accept melee DPS even though they work fine. Try learning the encounter before you cry that melee DPS doesn't work on it. By "try" I mean, go into it knowing it's possible and don't give up just because you can't faceroll it. It took us about a dozen failed encounters but we didn't have to resort to class stacking or terrain exploiting to beat it.