Yes, that is why I suggested maybe limiting this somehow in where there can only be a LW on the field OR one of these Cosmic Mages. It is a bit overpowered, yes. It also dies easily and has a very long recovery time. Like you mentioned, it would be great defensively, but so is a LW, but LW can't move.
I wouldn't want to see this as a unit, at least with the current description. It's a different idea though.