If Yasuo's windwall didn't block all projectiles, he would be a pretty terrible champion.
While it can be very annoying to play against, I feel as though it is a necessary evil that Yasuo needs.
His windwall isn't the problem, it is possible to play around it (literally) by waiting for the right time to fight, i.e. wait until he uses it before a fight then go in right after it is gone.
Also, the cooldown of it is already a significant number, even at max level it still has an 18 second base cooldown. That is longer than most teamfights last in League.