floyd can fight when he needs to, he just hasn't been forced to do so in his last couple of fights. there were times against ricky hatton where he was just stand and trade, not very often, but when he did he was just too quick and accurate. even against judah he was breaking him down until the low blow came, floyd was backing judah up with ease. against fighters like castillo and baldomir the clever thing to do was counter punch them till they lost their control and forgot what they were doing. when he fought delahoya he was boxing great of the back foot so there was no need to stand and trade. if there is a time in the fight where floyd feels he needs to exchange with pac he will, it might not come off but i don't think he will get too defensive, he is very clever at steeling the rounds and landing the more effective, eye catching punches.
Ugh, Pac is able to go toe to toe with the WW's because he makes up for his lack of size with speed and power, so if you take away Mayweathers advantage of his size and give it to Pac, I don't think it would be a fair fight then.