Thoughts ?
Yasou isn't dominating the competitive scene ATM like Azir still is.
At this point, Yasou is just a champion that looks/feels/smells/tastes/sounds OP but is objectively pretty balanced.
Same generally goes for counterplay and his overall design.
Subjectively he seems bad - but objectively his mobility isn't in the same spot as Trynd/Riven/Shaco/Fiora, his steroids don't encourage back-dooring 24/7, he's not dead weight when behind, his steroids are both surprisingly pretty weak compared to a wide range of other steroids when actual math is involved, he is actually fun to play with via knockup combos, etc.
Don't get me wrong - lanning against a Yasou as some of my favorite champions like Lux is often a massive pain, but I don't feel that's solid grounds for Yasou being unplayable. Having solid light fighter/assassin picks in the game makes it stronger as a whole.
And ATM: Yasou is right in pretty solid zone for balance looking at his play in worlds. He's not a 100% pick/ban option, he's just a ~3 games in 20 kind of pick with an ok showing.