Why is rengar not nerfed yet?

We targeted Rengar throughout the game he was probably 3/12 by the time he started doing anything, his bone tooth can't loose stacks, he did over 1000 damage with only unseen threat alone , i don't understand how this isn't a super op fact, he came back and ended up having about 1/3 of the other teams kills, and lead them to victory when we had a 20+ kill lead and a 5 turret to 0 at one point. We had every single dragon and they got baron once, yet we couldn't out match rengar. The least you could do is take his ult cool down off of a 20 seconds because that's how much he was seeming to using it. It's completely stupid how rengar is able to perform at such a level after being denied almost everything in the beginning and middle of the game. two big things could be done, longer ult cool down or stacks can be lost upon death, that's all he needs to make him a more even champ, riot please.