Yasuo can be fixed pretty easy, just take away windwall or make it last .5 seconds, for example. Easy fix, cancer champion becomes non-cancer champion. Why Riot won't fix things like this....
On the other hand, Zed cancer mechanics are not fixable. Without study or practice on the champion it is extremely hard or impossible to understand what he is doing and where the damage you are taking is coming from. Even if you understand it, it is extremely obnoxious to play against. To fix Zed would mean turning him into a completely different champ, in other words he should be removed from the game.