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.
Game mechanics have no effect on lore in vs threads, the only reason it takes 4ppl to beat Malgus is solely because the game wants you to go in a group. It takes 8-16 ppl to down Jarg and Sorno in KP, (ik some ppl have 2-3manned KP but some also have soloed FE) does that make those 2 bounty hunters stronger than Malgus? No that is purely game mechanics, you cant judge Thanaton or Satele's power due to their game mechanics, you have to go with their accomplishments and feats.
That being said, Thanaton has proven to be able to beat opponents that were far more powerful than himself against all odds (Lord Calypho and Exal Kressh). Satele has fought toe to toe with some of the strongest sith lords out there (Darth Malgus, Darth Baras) but has never beaten anyone noteworthy. I still give the edge to Satele as a grandmaster but i wouldnt count Thanaton out of the fight, it would be close.