Because he has one of the most broken abilities in the game, why not make it block everything so it actually requires skill. Why not make it block allied projectiles and abilities, instead of using it whenever he feels like and nullifying all ranged champions for 3 seconds. This champion already has too much safety and bullshit in the kit.
Or another option is, swap Braum and Yasuo wall effects around.
DuskDaUmbreon3 votesSo Braum leaves the shield in place, and Yasuo gets to move it around?
That sounds incredibly amazing for Yasuo.
After3perma2 votesNo I mean that Braum can block everything while Yasuo only blocks one then reduced damage.
DuskDaUmbreon1 votesNope, you have to swap all the effects or none of them.
Also, note that Yasuo's Windwall doesn't block anything Riot designates a laser or as a melee attack. 
's autos pass through it just fine. 
's E apparates on the other side of it.
ModWulf Helhammer2 votesXerath Q and Lux Ult as well. Also things that go over the screen, so Ziggs and Xerath Ult
DuskDaUmbreon1 votesThat too.
Basically:
Anything that looks laser-like for an auto. Anything that is a beam effect. Anything that appears instead of being cast or thrown. Anything that would go completely over the wall entirely (Except Soraka's Q).
AnAggravatedPimp1 votesCant block everything because trolling
Braum with Yasuo's Windwall would be OP unless he set an ice wall on the ground. Other wise it's a portable anti projectile shield.
PandaNator431 votesHow about just changing the duration and use Yasuo's flow as a resource?
On cast all flow is depleted. Wind wall last x base seconds, plus y seconds per z flow used to cast.
Edit: Add a clause: Wind wall can only be cast when flow is x% full. All those darn Yasuo players like dashing around so much. Make it a more important part of the kit :P