Everyone knows that maximum braking comes just before the tires skid. In Physics, the terms are "static" vs "dynamic" friction coefficient. That is the reason for "pumping the brakes", which anti-lock systems do automatically. Obviously, my point is that if drums can skid the tires, they have sufficient force to brake to the limit of skidding. It snows a lot in the Sierras 60 miles away (heard of the Donner Party?).
So your main claim is that one gets more delicate control of the braking force with disks? We need data.
As mentioned by others, in road racing (constant braking on turns), the faster cooling of rear disks could be an advantage, otherwise no concerns w/ rear drums.
