The problem isn't Yasuo - it's lifesteal
Yasuo is actually fine. If you get past his shield he can be easy to take down. He's annoying to play against but he isn't super strong. The problem arrises when he has 100% crit WHILE also having a shit ton of lifesteal.
Because he's so DPS based he will effectively have 2x or more of his hp pool in health.
He becomes ridiculously tanky when he has
and gets the potential to 1v2 or 1v3 when ahead.
alone gives 20% lifesteal. If he does 500 damage per hit and 2 to 3 hits per second it means he heals 500x0,2=100 = 200-300 health per second healed. This is assuming he does 500 damage per hit and only has 20% (he can get more easily) and also only does 2-3 hits per second.
If you add in his mobility + AOE damage with Q and windwall he becomes extremely obnoxious to be dealt with.
TL;DR I believe that Yasuo isn't the problem but lifesteal combined with his DPS nature is.