Also in constructed the issue is vs agro deck, they will play a lot of card and maybe can force you to run it into a 1/3 taunt.
And vs control deck well they are already use to deal with a 8/8 giant on turn 4, he is 1 turn later. Big game hunter, SW:D just crush him. Also just putting a Sludge Belcher, make u discard 3 cards and eat 8 damages. A doomguard is scarier imo. Ah aslo sapping him is funny :p And for all people saying cards you discard are not important. Burning a kill command or that kind of reach is a big deal, how many game agro wins by just by topdecking your reach. Maybe he can be use in paladin agro or another kind of agro deck but i doubt it is gonna be warlock or hunter.
In arena you need to be ahead for him to be good, or on an empty board. Yesterday i mill 9 cards in 1 turn, killing him with 1 card in hand and 1 minion on board and i just put 2 more minions downs.