Needs Rengar to be nerfed?

I think Rengar should be nerfed at some points, but at the same point he needs to get buffed. I think Riot already did a great job by making it harder to over/underlevel. But with assassins like rengar,kha'zhix or zed it is over when they have a gold advantages of you and they buy duskblade before you get something like zhonya's. Rengar is at the moment with his ult to the most adc a point and click kill. Not much skill required. When i played as Alistar i even saw ashe build zhonya's once. In my point of view rengar's passive should be changed. I would say that the first 3 points require less stacks and that Rengar gets them after a certain point in the game but after the first 3 the stacks required should be way more because with his W in a teamfight he mostly gets much assists/kills and with only 20 stacks for his passive to be fully stacked i think that is way to OP. Is this just my opinion or are there more people who think Riot should do something about it?