Imo mute was perfect in AC:B. It was fairly easy to avoid whilst being fairly effective to defend with. Your target was always able to flee before you could stun/kill them, and getting on a wall was an instant avoidance technique. It's long cooldown balanced out the fact that against newer players it's an instant stun/kill ability, and it was vital to breaking up stunlocks in alliance. It could just be because it's one of my favourite abilities, but I've never had any problems with mute being in the game.