Today a Yasuo, after getting oneshot by my Malphites "Unstoppable Force", wrote this:
"WTF I WINDWALLED????"
Plat ELO. Just saying.
Trust me, it doesn't matter how op you think Yasuo is. The people playing him make more than up for that.
AstroFerrari 2 votesLOLOL
A Doorknob2 votesLol be hilarious if Malphite got instakilled because he's a projectile under those circumstances.
The JigSAW1 votesRock solid point. 
Martensitic1 votesnot just killed, completely removed from the game :D
The JigSAW1 votesBecause they can't win or do well with other champions if they pick him. Most of the people I know who use Yasuo can't go positive in half their games without picking a really easy champion with a regenerating shield in combat, a wind wall, double crit, 50% bonus armor pen for 15 seconds on ult, a 0.5 sec E cooldown at rank 1, etc.
Would be a terrible shame if a champion was coming out shortly who could block a Yasuo into some kind of structure around the turret he just dived and deal true damage basics, huh? -sips chamo-Camille tea- 
Martensitic1 votesBecause they can't win or do well with other champions if they pick him. Most of the people I know who use Yasuo can't go positive in half their games without picking a really easy champion with a regenerating shield in combat, a wind wall, double crit, 50% bonus armor pen for 15 seconds on ult, a 0.5 sec E cooldown at rank 1, etc.
Yeah but here is the thing...they also can't do so with Yasuo, more often than not ^^
The JigSAW1 votesI go by two simple rules for a champ if they are "broken" rather than just go along with everybody who says they are.
Basically if the answer to both is yes, the champ is broken. I know people who have a hard time with mages and assassins, they tried fighters, end up using yasuo or yi and surprise they get 25-30 kills a game.
Plat ELO though? Lucky. I'd love to learn more from higher elo people!!
Martensitic1 votesYou are overlooking the most important fact however:
No matter how far ahead a Yasuo gets, he will, inevitably. go yolo 1v5, die and give away free dragons/barons :-)
The JigSAW1 votesSeen it many times. So focused on kills they forget the actual concept of winning is NGB - Nexus go boom! Turrets, dragons, barons, inhibitors are more important than how many pentas can you get. The new Ask Riot said Yasuo nerfs are incoming so thank Nagakabouros for that 