I can see Marquez looking that much different just by adding weight training, in one form or another, to his regimen. My whole life, I worked out and stayed in shape. Since my by-pass surgery (and once my chest healed, and probably to strengthen that weakness) I have started using more weights and direct resistance exercises in my workouts. I am finding muscles in places I never knew I had them before, and I drink more beer weekly than Marquez has probably drank in his life and am coming off 16 pretty sedentary months post surgery.
Now, whether those extra tummy muscles make Marquez a better fighter, NO. What makes him good is the knowledge Nacho Beristain imparted to him, and what he has learned in the ring. Him koing Pac was inevitable; the guy was there to be timed and I am suprised it took him so long to do it.