Brakes work by creating friction, the friction converts the energy of motion into heat energy. The breking system needs to dissipate all the heat quickly and effectively to function. Once a braking system is so hot it can’t get rid of more heat then it “fades” meaning it can’t brake any harder because it is at it’s heat capacity. Disc brakes can dissipate a lot more heat faster than drum brakes. Therefore disc brakes don’t fade in general.
The power of a braking system is proportional to the amount of surface area of the “friction material” The more surface area where the pads contact the rotor, or shoes contact the drum, determines how much stopping power you have. Drum brakes have a lot more surface area than disc brakes. Therefore if you need to stop a heavy vehicle faster you can engineer more braking power into the same size wheel with drum brakes. This is why most heavy trucks use drum brakes. The trend to larger wheel sizes in cars is driven by getting more braking capacity on the car using disc brakes.
Another difference is how the brakes work when wet. Discs brakes are an “open” type system. They get wet easily but the water spins off the disc instantly and the friction of applying the brakes creates heat quickly that burns off any remaining moisture instantly. Therefore wet braking performance is almost the same as dry braking performance.
Drum brakes don’t get wet easily because the shoes are enclosed in the drums. However if you submerge the brakes going through an area of deep water braking power is severely impacted. Once water is in a drum brake it takes a while for the water to drain out. During this time little heat can be dissipated and therefore the braking power is only a fraction of the normal braking power. Eventually they will return to normal but this could take minutes instead of seconds.
Since large vehicles have bigger wheels they are less likely to get wet. Proper engineering can reduce the brakes exposure to moisture as well. Therefore drum brakes can be excellent systems in suitable applications.
So if you need more braking power, advantage drums. If you need to reduce brake fade, advantage discs. If you are driving through areas of deep standing water frequently, advantage disc brakes.