Well, the bigger one will, of course. So if all other things are equal, the big muscle outperforms the small muscle. Because now the rules have changed, or I should say the performance limitations have changed. When we put the muscles back inside a real body, neither of these conditions are true. When a bodybuilder trains, the goal is to make each muscle fiber as big as possible.
Muscle fibers have contractile protein, mitochondrial protein, and other components.
From an endurance standpoint this is not a good adaptation. We even give it a name in sports physiology circles, mitochondrial dilution . The bodybuilder's muscles may actually become more easily fatigued as they get bigger, because their mitochondrial density is not increasing at the same rate. The bodybuilder accepts that because the name of the game is size, not endurance. It is possible for the endurance athlete to gain some muscle size and maintain mitochondrial density, but it requires that the volume of endurance training be maintained.