If Galio's E (Righteous Gust) creates wind that flows in a direction and speeds up allies moving in that direction, why doesn't it also slow enemy trying to walk in the opposite direction? Could be a nice buff to Galio. :)
Because his Q slows. Honestly if Riot is going to buff Galio they need to make his Q more impactful, and preferrably more reliable.
His e should be a knock back honestly
Probably because his Q already HAS a slow.
Even if you take Q's slow and give it to E, what does Q do? just damage? That's kinda lame.
Because all champions are extremely aerodynamic in the direction they are travelling.
Well, let's go over the champs that have stacking abilities like that (two of each type of steroid or crowd control)
two attack speed steroids
two damage steroids
two attack speed steroids
two damage steroids
two defensive steroids
two movement speed steroids
two slows
Notice anything about those champions? Most notably, their kits? They're quite bad aren't they? When you stack the same effect on two abilities, it downplays that effect. It's part of the reason why these champs are in such a bad spot right now. Sticking a slow on Galio's E will make him even worse than he was before, because that extra slow will come at the cost of some part of his kit.
also makes reksais burrowed shoot thingy slow
The only problem with Galio is 
and probably a couple others I'm forgetting right now. His ult it just canceled way too easy by a roster of very popular champs that you're almost always going to be matched against.
How to make Galio competitive:
Make E's width wider, add this buff to it. Remove Q's slow, add a debuff that reduces magic resist (first thing that came to mind, similar to Karthus' Wall, but a lower percentage)
Give his ult's re-activation a short knockback (say half the range of Vayne's condemn), or a knockback that scales with how long he charges the ult for.
I was going to add Ranged AA's, but that would probably force Riot to remove his scaling MR in exchange.
Because we don't need any more slows in this game when like 70-80% of the cast has them
