I disagree that it's arguable:
-While Fedor was a phenomenon and one of the most exciting fighters of all time he fought mostly marginal opponents in fringe organizations and never reached the pinnacle, you can't say Taro Tsujimoto was the greatest hockey play ever no matter what because he never played in the NHL
-Silva fought every competitor the UFC gave him for 7 years and hasn't lost once, in the top organization in the world. No one has come even close to that. You add on the fact that he willingly lets his opponents have dominant positions, which nobody else does. He's just so far ahead of the pack that it's not even close, atleast when trying to look at it objectively. I never even really liked Silva for most of his 7 year run
I mean, how is it subjective?