Yasuo's kit makes him unfair to play against
My 3 principles of balance are: Mobility, range, and damage. Yasuo has all 3.
First of all, his e makes him super mobile even if there are no minions in a team fight. Fine, other champs have mobility so moving on.
Next, yasuo has damage. He is an ad squishy like trynd and fiora, fine. Starting to become op sounding...
Finally he has range in the form of a third q. If his broken e wasn't already used, he can ult in for a gap closer. Yes it is a skill shot but eventually one will hit someone in a team fight. There it is gg.
An extra to add is his windfall if skillfully used can negate most engages... He just has too much in his kit to balance and that is why he has consistently been hated. Once ahead he will stay ahead unless heavily throws...