I understand the Yasuo QQ and don't understand it
Yes, I play Yasuo on occasion. Only mastery 4 on him, since i don't play him too much but he's fun to play.
Now about how his playstyle can be very toxic.
Me, being a Gnar in top lane, it's very frustrating to fight against a Yas, he can E out of my Q, block it, and have extremely mobility and rape me early game since I don't get a major powerspike until I get my Mallet. He is frustrating to play against.
How is he overloaded? I wouldn't say he's exactly completely unhealthy, but he's very strong. From my experience, I've seen Yasuos go 1-5 early game, then pick up 100% crit and iE, with some type of Lifesteal and start carrying. I see him as a Nasus, i can rape him early game and he'll just comeback harder and stronger, but that isn't a guarantee. Games can early, Yas can't get his required items, etc.
From this being said, he's not exactly "OP", but he's in a relatively good spot but in the hands of a mastery, it's extremely frustrating.