Hearthpwn

Kil'Jaeden isn't as powerful as you think. Drawing and playing one increasingly large guy per turn isn't actually that great, as far as top-ends go. You spent a turn playing a War Golem and your next several draws will actually be worse on average than the cards that were in your deck. Many decks have stronger plans to outright kill you, or can just swing board and aggro you down if you don't draw a few specific defensive demons. He'll close out a game about as often as the Golden Kobold you shuffled in with Marin, which is like, I've seen it happen. But it's not usually how things go. He's substantially better in warlock because you get two demons per turn with lifetap + Foreboding Flame.