Well yes, if those boxers you mentioned theoretically won every fight, some of them would have records equal to or even arguably surpassing Robinson. As far as their chances in actual h2h fights, I don't think Duran would ever beat Hearns in 10 attempts. If I had a time machine and managed Duran, I'd do everything in my power to avoid that fight. Every other loss could have theoretically been reversed with a different game plan/conditioning/mind set etc. Really can't see Pac beating Marquez 4x. Likewise, Mayweather would be one hell of a hurdle no matter when the fight took place. Jones absolutely could have beaten all his opponents. Some guys he lost to had no business being in the same ring. Holyfield is really tricky. The guy had so many mixed results and letdowns despite always being in shape and giving it his all. I think the biggest obstacle for an undefeated record would be Bowe. You could argue that he lost all 3. Beating Lewis twice is also an insanely difficult task.