So far I've noticed that even if people do the bare minimum with the cannons (even miss one or two of the dragon killers or w/e) if the group has two competent melee you can still faceroll the fight fairly nicely. I don't usually do the roulette anymore but one time I queue'd on a whim, people were using the cannons to kill the adds and were kinda fumbling on the stuns/snares but myself and the other melee stayed on the boss and we managed to just burn him down and kill him in a oneshot right before he made it to the end XD.