Take a fighter. Match him up hypothetically with every single fighter in the top ten of their weight class. Take the average of the gamblings odds for each match up.
The best fighter in a weight class is the one with the best over-all odds. The best fighter P4P in the world is the fighter with the most tilted odds, at least for ranking purposes.
The reason that Fedor is the number one fighter in the world is he'll get MASSIVE odds in his favor against any heavyweight in the world. Gonzaga? Couture? Arlovski? Barnett? Nog? Cro-cop? He'd probably get above 4:1 on every HW in the world.
Hughes? The odds would be AGAINST him or next to even versus the top 5 welterweights in the world. Gomi wouldm't have nearly the gap fedor has. Anderson Silva and Hendo are in the same situation.
NO ONE can even close to producing lopsided odds like Fedor, no matter what you adjust for ("styles make fights","TUF audiences' ignorance","the hype from the nuthuggers", whatever.)
It's far from a perfect system, but it's a better system than people just throwing around their bullshit speculation about who they think would beat who.