Not only do Leaders often feel like "Controller Lite", the Arcane Power Source often has very "controller-ish" powers.
I think you'd have to take some powers and maybe reskin them. You might also want to come up with some new powers.
One thing that strikes me is the idea that the music would have the power to cause the attacker to miss with a weapon or power. I like this. There are a couple of ways to do this, I'm sure. My first thought is to have a Trait wherein any attack with the Weapon keyword would actually be rolled against Will instead of AC (or whatever other defense they may target). Presumably, Will would be the highest defense. Or perhaps the Trait would give a penalty to any attacks with the Weapon keyword as long as the target is playing music.
The concept of the bowing of strings accelerating their heart could be done by a Close burst power that targets Will and a hit causes the loss of a healing surge. And, as per the system, if there are no HS left to lose, they lose hp instead.
You could do other powers that would cause forced movement, making them dance in a particular direction. And possibly have a power that would Daze the target (Save Ends), since the music is directing their attention away from the battle.
I'm thinking that some of these powers would have the Charm keyword. They probably would all target Will, too, as that seems to make sense.
Anyway, these are just some of my first thoughts.