I guess the distinction of being the man at a respective weight class. Floyd doesnt have all the belts and as a result is not really undisputed pre se but he's "The MAN" at 147. Same with Calzaghe at 168, Pavlik at 160, Wlad at HW.
No, Floyd is not "The Man" at 147. He is (merely) a bankable superstar and P4P number one, but he has not proven himself the best in his current weight division.
I think in Charles' case, the assumption was that he would have been champion, had he been given a shot in the late 40's. That's borne out by his five victories over Maxim, three over Moore, and reversals of the losses that he suffered to Marshall and Bivens earlier in his career. Charles doesn't fit into this particular occasion because he never got the chance to win the title. Had he done so, he likely would have enjoyed a pretty lengthy reign before moving up to heavyweight.
But he is not, and does not qualify for #1 because he decided (probably financially wisely) to move up to Heavyweight...
Thing about Charles though (if he fits Fighter B), he did beat Mooore (who could resemble Fighter A) three out of three. If something like this appeared in opening post then I'm sure many would have gone for Fighter B as the better man.
Obviously fighter B is better since apparently fighter A blatantly ducked him for years knowing he wouldd get the pants beat off of him if he ever stepped into the ring against B.:good