An idea I had to fix McCree

So McCree is insane right now. I'm not going to go into detail as to why, but the Stun-Hammer combo is simply too reliable and powerful.
So I present to you my idea for a nerf:

Have the stun's duration fall off depending on how far away from the grenade the target is.

Imagine if Pharah's rockets always dealt 120 damage, regardless of if she hit dead on or within the splash radius. That's McCree's grenade. This would make him harder to play, and far from as powerful against Genji, Tracer, Reinhardt etc.