If I was going to do some tweaks to Yasuo the first thing I would start with would be his ulti.
Lets take a look at this ability

See how ridiculously overloaded that ability is? Does he really need all of that? No
Does this ability need 1200 range to be used effectively? No
Would nerfing the range affect his gameplay significantly? Not enough to make him unplayable.
Does this ability need to work with other knock ups? No
Would increasing the CD at later levels nerf him enough to hurt his place in the game? No
Another thing would be to remove the maximum flow upon arrival because a big problem with Yasuo is that he is too tanky for what he does.
None of these changes
alone would make him unplayable but would hurt him enough to where he is less excruciating to play against. Yasuo isn't binary enough to where changes like this would make him unviable.
If he is still problematic after that I would look at his passive shield.
Most people seem to think wind wall is the problem with that champion when it really is his overloaded passives and ulti.