Maybe they will never fight each other. Floyd could fight Martinez, then some other champions or beltholders, then retire in two or three years (undefeated). And some could consider him in the Top20, Top15 or even Top10 of all time. Same could be for Pacquiao, maybe he will fight some champions at 147 and 154, and end up in most people's Top10 of all time. Could it happen? I mean...Could Floyd and Pac, both, end up in the P4P Top10 of all time without fighting each other? It would be epic, a fight between both would be THE fantasy matchup.
Pacquiao and Mayweather really can't move up the all-time great list unless they beat the other or beat Martinez at a reasonable weight. Beating the Alvarez's, Khan's, Ortiz's, Berto's, Bradley's, Lara's, etc. of the world doesn't really mean much. All of those guys are basic fighters and not noteworthy in the bigger picture.