This would be beside the fact. You have claimed the quads are not used while the glutes and hamstrings are dominant. Stay on topic. Merckx doesn't have massive quads, but his glutes and hamstrings are smaller still. Cycling allows you to exchange torque for speed. But we aren't talking about leg size, we are talking about muscle dominance.

As far as the rest, it is well understood that cyclists develop fairly large muscle imbalances by only riding their bike. Every cycling coach I've met has some program for off-the-bike work as well as on-the-bike drills to augment straight riding.