What would Yasuo do if he didn't have windwall?
Nothing, he'd be fucking useless. Why? Because if he doesn't have that bit of utility, then he's complete shit if he's not ultra fed. And provides nothing for a team. He needs it for defense he's a squishy melee character (second lowest base stats in the game). Who relys on AA's to kill people, if you were to take away Wind wall, you'd need to give him something else he could use to provide for his team when behind, while also being defensive.
If you can find another thematically correct defensive ability that provides utility as well for his team. For a melee squishy assassin. Then I'll gladly hear you out. (it also has to fit with the rest of his kit)
P.S. Don't Just spam Yasuo main in the comments, that contributes nothing towards the conversation :D

also needs a windwall. He is a squishy melee, AD carry that relies on AA to kill enemies. He provides nothing for his team defensively wether behind or ahead. Give master Yi a windwall!
ult/heal
Riposte
windwall