Could be 3 melee dps but with different rotations and type of damage: a high dps weapon damage specialization, a DoT specialization and a burst but lower dps specialization. And maybe one of them should be better to kill multiple enemies.
Maybe could be interesting to add him some support abilities but skills that support the tank, something like increase the tank resistance, increase the tank aggro, reduce the aggro of a member of the party, reduce damage taken by the party. Something like throw a flask to the tank to buff him for a while.