Abyssal Drain is not useless......if you were any what of a good tank pulling 3 or more mobs and tanking you would notice with Ilvl 170 your drain does 300 damage to every target you hit without a crit so if you have 3 or more enemies you are doing 900+ damage a tick compared to a non crit buffed souleater for 900 on single target. Dark Knight is a tank...not dps! I do not understand why a tank with such a amazing ability wouldnt want to continually want to use the ability on 3 or more targets with your dots applied to all targets, salted earth down.....and aoeing all enemies down while keeping aggro so they all die evenly while you dps aoe themselves or burn one a time to when they do single target the mobs they are already severely injured making that pull even faster. Stop focusing on single target rotations with the mentality that Dark is a melee dps and use all your abilities to make pulls faster and more efficient as a tank should.