Yasuo has the second lowest win rate, 1% above Urgot in his current state. With my previous matches as Yasuo, I noticed that he has 2/3 of the health of a regular Madc; the only other champion with lower health is Sona.
He is fine. People only think he is OP for the sake of thinking it.
The same goes for Tristana and Karma, so many other champions outclasses them in their respective roles. They shouldn't be on the priority list for nerfs.
The only champions I agree with are Katarina and Akali. Their main issue is that all their skills are point and click with some of the highest bursts and mobility in game. This allows essentially anyone to do as well on them as on a harder champion such as Ahri without as much practice.
Nasus is in a tricky situation as of now, he is either extremely good with his Q at 600 stacks, or not. Before achieving 600, one could argue that he is under-powered. He should definitely be changed, but not nerfed.