For PvP, full Darknesss spec is considered subpar in terms of control for ranked. We have a good amount of control (Electrocute, Spike, Mind Trap, Overload, Whirlwind) But we lack an AOE mezz like the PT (Carbonize) and Jugg (Intimidating Roar) . Because of this we are vulnerable to high burst hard switch comps. Which everybody runs. If you are playing againt DOT specs though, Darkness does great.