It should do friendly fire to be honest. It would still be s-tier. It would still be a complete no brainer must have skill for every build that uses a melee weapon.
This was probably play-tested and discarded. Singleplayer you can work around that, but think about multiplayer. People would constantly stay in each other ways, making the skill a no-go or even worse, player stun each other constantly (either because that is the best tactic or they don't care).
Magic spells have quite some friendly fire, but they are either single target or you can place them wherever you want.
So for short, I don't think any spell in the game is overpowered as of right now.
