Why not make Sion Invulnerable to CC while he is in his Q animation?

You won't give him a swivel on his Q. You won't increase his Q damage You won't make it faster to use

So how about you just make him invulnerable to CC while his Q is up? That way the only thing people can do is run away from it, a true zoning tool. Right now people dont even bother running out of it. They just sneeze on you and its interrupted.