The size difference is only relevent based on where they have spent their time fighting. JMM is jumping up 2 weight classes for this fight, Floyd is fighting where he's been for a long time. Even tho he won 2 lightweight fights, IMO JMM @ 135 was losing some effectiveness, be it from the added weight, getting older or both. This 2 class jump is a big deal and favors Floyd greatly. Mayweathers long layoff comes into play too but if JMM wins this fight, it will be a huge, huge, victory making him #1 P4P.
Fight promoters really has that ability to portray mismatch fights as competitive fights... Fans should appreciate that... .