That's what I noticed too. In the past few fights, JMM looked like he was pretty bulked up and strong but he still had a slight fat roll around his waist. He reminded me of an older guy trying to muscle up but was just not able to hit that "peak" level of conditioning anymore.
Yesterday though, JMM looked like an athlete in his 20's. He was very lean, muscular but lean, much like a sprinter or a triathlete would look like. There was no fat at all around his waist or anywhere else. His muscles looked very compact and solid like fast twitch muscles have been the focus.
Pac looked like he was sporting a little more fat but not much. He looked solid in the mid section but his stomach is always laden with lumps of muscle everywhere from all the stomach conditioning he does. His arms looked smaller than JMM's did (the shoulders especially). Pac actually looked bulkier than JMM did to me and JMM looked like he would have the better stamina.