Somewhat wrong Bodyfat is mass and mass is an important variable in power. Carrying that not quite but almost worthless fat around doesn't hurt furys stamina so its no big deal. Wilder should get some fat on that body...without it he stands no chance against the heavier fury.
And there's a reason, it's called beer. Sanders admitted that he trained maybe 3 hours a day at best then went to the pub. Guy was a beast though, think what he would've done with some drive in his heart.