Yasuo is weak at the moment, sitting around a 47% winrate on the websites I've looked at. However, the problem isn't his damage, the problems is his counters. People like Nautilus, volibear, and janna are running rampant with 52%+ winrates, completely negating yasuo's main strength, mobility. Many of the strongest champs these last few patches have undodgeable disengages, engages, or crowd control, and with a decent team, Yasuo gets blown up during this cc. I don't know how many games I've played this season where i go 4/1 or 5/0 in lane, just to lose the game 5/7 because their bot lane got fed and had one of these champs. I personally call these champs the anti-one man carry champs
Because of this, Yasuo brings very little to teamfights compared to Orianna, Anivia, Ekko, or many other mid champions. If the other team has a good utility support, you have little chance to have major inpact on the game. Yasuo can be useful in a teamfight, but others can do similar actions much safer than he can this season.
I can't think of a buff for Yasuo that wouldn't make him either super op, or just make laning phase easier without solving the problem, Honestly, we just have to hope Riot nerfs these champs. Maybe buff his resistances so he doesn't get easily killed after Naut desides to hit R.
