More competitive. Mosley had excellent power at that weight and was at his quickest. He also never lost there so he had a confidence there that would mean he was much more likely to be on the front foot and looking to dominate. I think this would be a close fight and Mosley might actually win it.
Tho still in good form Mosley was all but 39 years old. It would be competitive at the very least imo.
Mosley was a shell of himself by the time he fought Floyd. Although I feel like Mosleys speed left him rather early in his career but say the Mosley that Delahoya in their first fight would be much closer fight. W Floyd the winner.
In their WW fight, Mayweather proved that he was technically far superior than Mosley. He beat him with brains. Superb timing.
And there's past prime unmotivated Mosley and peak 135 Mosley. If a worn out De La Hoya could do that to Pretty Boy, imagine what prime Mosley could do.
I'm not sure to be honest, on paper Floyd should win but it's been proven, sometimes by Floyd himself, time and time again, that even the best defensive operators can be tagged by speedy fighters. There's only so much technique and skill can do before athleticism takes over. Mosley's competition at lightweight was really nothing to speak of, but he dominated most of it. Against a big money fight with Floyd he surely would have risen to the occasion. And I'm sure Floyd would do the same. I think it would be a very controversial decision in which Floyd wins most of the rounds but only barely, and Shane wins the few rounds he does in a big way. I usually prefer the role that Floyd would play here. SD Mayweather
Both fighters looked their absolute best at or close to this weight class. But I'll slightly lean to Mayweather Jr. I feel he was just more adaptable than Mosely. Even in his prime Mosely didn't adapt when his plan A didn't work. He never came from behind to win a fight that I recall. That's were Mayweather jr beats him, because he could adapt and change fight strategy during the fight.
Mayweather would have his way. Mosley's aura of invincibility at 135 was due to fighting C level opposition.