Fedor represents the best amongst current fighters, undoubtedly. Notwithstanding, he cannot claim the title of greatest combatant ever because there is a rock that he would need to remove for him to achieve that: Mister Rickson Gracie, who is the de facto greatest fighter ever, having 450 professional wins with no defeats.
Also, I believe that Wanderlei Silva in his prime when he fought at PRIDE would defeat Fedor. After all, he did knock out Clinton "Rampage" Jackson in a couple minutes. Saying that Wanderlei knocked him out is an euphemism: Silva almost killed him.