Parlaying your advantages into actually making them effective IS a part of being a good fighter. Your op is basically like saying "Anderson only wins because he's faster and has superior reflexes. Let him face someone with those same attibutes, THEN we'll see how good he is." "GSP only wins because he has a faster double than the rest of the division. Let him fight someone who equals that THEN we'll see how good he is.".
The aspect of Jon Jones you are questioning isn't how good of a fighter he is, you're questioning his fortitude. If we were measuring who has the P4P highest will to win, then there would be some question marks because he hasn't been tested. But because he's dominated most all of the best fighters in his weightclass, then I think it would be safe to say that that would be apart of establishing his legucy.
Otherwise, all you're basically saying is "Well, he's only the best because he's better than everyone else. That doesn't mean anything!".