Malgus's feat against the strike team leads me to believe he could replicate destroying Thanaton with ease. And Malgus being considered one of Sidious's most powerful predecessors, saying his feats on the battle field haven't been replicated, and actually having traceable showings of skill as opposed to vague quotes have me placing him on a somewhat higher level than Marr whose only showing is beating Lachris and killing fodder warriors. Its probably not a stomp considering their comparable accolades, but Malgus has better showings with the lightsaber