It is a 15 second cooldown?!! You think that is bad. If you are on a team where someone else can slow and has stuns, not taking repentance would be stupid. There was a reason you wouldn't take improved Hammer of Justice before when you played with a warrior. It DRed too much of his cc to be worth it. Even with the cast time the Repentance on a healer to kill his teammate is still there. With your logic than cc like Fear and Polymorph are useless because they are casted. No you just find the right opportunity to use them like all cc.