Medic Uther was still very distinctively Uther, just with customized medic power armor. It didn't intrude on the medic fantasy or silhouette too much. Same with Azmodan having a Gul'dan skin. They're very easy to tell apart. You can't tell apart Widowmaker Nova from a regular Widowmaker just like you wouldn't be able to tell regular Magni apart from the Muradin Magni, so you can forget about them ever adding Widowmaker or Magni to the game.