Yea he looked less muscular to me especially in his back and shoulders. He's always been deceptively solidily built, blocky.
One way i could see mayweather struggle is if his reflexes have gone. 2 years out and 40 years of age it's very possible his reflexes aren't the same. Like Roy Jones whose reflexes went over night he started getting caught by shots he used to be able to pull away from. It's the punches that you don't see that do damage, so if his reflexes have gone and he's unable to get away from shots he could be lights out. He like Roy relies a lot on superior reflexes.
Not that I think this will happen, I think conor has less than 3% chance to win. But if I was to think of a way he does win it would be above.