Thats why I said almost :P In the first fight, it was sub-50 PvP so lets not go with that. The second fight was close and Jace only got a grenade off. My sorc steamrolled through Thanaton and I needed the Wrath of the Emperor, the Grand Champion of the Great Hunt and Cipher Nine to kill Malgus. If Satele could either solo or two man Malgus, but Thanaton is soloable, yeah. Besides, Malgus is a boss and Thanaton is not.
Or you could say that Satele solo Malgus because Jace is only a companion.