As in instead of staying fat year round and cutting water weight to make weight.
DC could instead actually cut the fat and become ripped so he either doesn't have to lose so much energy trying to cut all that water weight.
Or he could both cut fat and gain muscle. That way, he will actually be stronger and more in shape, instead of fat. Is it laziness? Undisciplined? What is it?
A. DC isn't actually very "fat." He was fat(er) the other night, yes. But he has a very thick, dense, torso. At his very leanest, he would still look like a cinder block.
B. DC is extremely strong and well conditioned so the extra fat that he does carry around (and there is some) doesn't slow him down. An extra 15 lbs on a strong, well conditioned, athlete has very little negative effect unless you are running of biking for distance.
C. Extra weight around the midsection can actually have some distinct benefits. For one thing, it helps anchor the body when standing still and increases the momentum of the body when moving forward, both of which translate into greater punching power. In grappling exchanges it can give you better balance and much stronger hips, and can also make you hell to get a good grip on.
D. The best versions of DC that we have seen are the "fattest" HW versions.
E. DC's primary difficulty against JJ is overcoming the reach advantage. He's not going to get any taller or longer by losing weight. He will just get easier for JJ to get a grip on and bully around. I know you are suggesting he replace that weight with muscle, but that isn't as simple as you make it out to be since people tend to lose strength and muscle when they shed bodyfat, and even if it was, an abundance of too much muscle has proven counter-productive in combat sport.