[B]Warlocks are a Pure DPS pet Caster class, with a focus on Pets and Dots. Demonology using the Tanking Build (click For Demonology Tank) is still a range casting spec, which can tank and take a hit without getting damage. DemoTanks which is something I play are tanking from the caster mind set, I have 0 white damage, and 0 need for moving unless I'm near AOE, I jump into battle and never once use stealth.
Demon Hunters are Melee Casters with Stealth, They sneak into battle from shadows they dot and curse as the auto attack with a sword in each hand. They can tank but they use Evasion and avoidance as the damage mitigation Unlike Demonology which become an unmovable rock. Demon Hunter would have to stay moving as they play, they would have to wear mail armor and would only be able to use Bladed weapons. Now I see how you might be afraid of this class since right now you tank in the same method as a Demon Hunter, however you would not be competing for gear except weapons. Since a Demon Hunter Class would come in wearing Mail, the Healing Spec would use Shaman Healing gear, the Tanking and DPS would compete with hunters for Agility Mail. This in no way would hurt anyone's game play, and if you think Monks are the best class I am sorry for you because every class is the best class. I play Warlocks, Monks, DeathKnights, Hunters, Mages, Warriors, Rogues, and Druids. -Never liked Shaman, Paladins, and Priests.