So yasuo a controversial topic
In my opinion hes the worst thing to ever happen to league of legends no matter the numbers his kit just isn't balanced, however ill try to be as unbiased as possible while i try to break down his problems.
His passive - Yasuo gaining double crit is a mechanic that is fine but he doesn't rely on critical strike to do damage which is a problem. People building items like black cleaver or trinity force and still being able to assassinate squishy targets. His damage could just be reduced to rely on critical strikes more, which would nerf his powerful early game to a similar level of the weaker early game champions.
His EQ combo - i simply think that this ability is way to easy to hit and the damage remains the same as his normal q i just thinks this ability needs a bit more counterplay
His ultimate - well i think the way his ultimate works is fine, but the armor pen is really crazy and using his eq makes it way too easy to land.
these were complaints i have with him id like to see him nerfed in some way because hes kind of a problem in my opinion.