In what other sport do you judge a performer or team with a lesser record against lesser opposition to be the superior? This is simply leaving all real world evidence behind. I would say the thinking here is closer to a religion than to a science. It is simply a belief based on personal faith.
But then it wouldn't be a fantasy match. Also it isn't just fighting inferior opposition. A man undefeated against lesser opposition is simply unproven. One can't be certain how good he might be. Ali before the first Liston fight is an excellent example.
What is the point here? If A has an inferior record against lesser opposition than B, and then loses in a match with B, is there any basis at all, and I mean at all, in judging A superior?
To win this head to head argument, someone needs to convince me that the Willard, Brennan, Firpo, Fulton which Dempsey faced were a better lot, in a head to head sense than the Walcott, Charles, Moore and Louis that Marciano faced... and that hasn't been done.
With Jones, we can at least decide to which degree to factor his wins at 168, 175 and heavy. With Dempsey, there are no victories in other weight classes. Still, in beating two future champs at 160, Roy did about as good as Dempsey who beat one former and one future champ.
So what do you believe and what don't you believe from him? How do you pick and choose? He's clearly been shown to make up stuff as he goes, and frankly, I take some of what he says with a grain of salt. He was in the business of perpetuating myths and stories for his own financial benefit many times, not in the field of finding the truth to perpetuate