Brake fade under excess heating is absolutely a thing - when your brakes get too hot their ability to decrease your speed will reduce. Doesn't matter if you've got disks, rim brakes, a drum brake, a roller brake, a coaster, rod brakes or a spoon brake, they all lose performance as the temperatures rise.
A Long Paved descent is no different. As a rider you can choose to pedal or to coast, you can choose to be aero or sit up and catch the breeze. Much of this comes down to line-of-sight and your confidence level.
A long sustained slow drag on the brake will raise the temperature of the pad and its brake surface, and hold high. The higher temperatures means less "headroom" before the brake overheats and function is reduced.
Heat will also "soak" further into a rim, potentially upsetting glues, patches and sealants in the tyre, which can be bad for a glued-on tubular like the pros often use.
By comparison, a hard brake of a second or two duration, followed by a similar length of no-braking will keep the overall temperatures lower. Alternating between front and rear allows you to cap your speed, and reduce runaway. While one brake is braking, the other is cooling.
The system "bicycle plus rider" is notoriously hard to model well. So many models must simplify something, potentially going off-course. As a rider, you should consider testing on your own bike. Find a descent that is 5-10%, and ride it once a weekend for a month, while recording your rides on something like Strava. Alternate your methods and see which one feels best to you. Too shallow and it won't show the braking effect. Too steep is unnerving to ride down fast.
Better brake pads can be the easiest fix to brakes that heat quickly. Kool Stop is my go-to brand for everything now.
I've experienced brake fade twice. Both were rim brakes.
First time was a MTB with cantilever brakes, on a -19.5% average gradient in dirt and shingle in 11.6 minutes descending 219 metres. The brakes faded so much the levers bottomed out on the bars and I was still accelerating. The track pitched up, so I stopped and checked the rim temp, and it was very hot even through gloves. This was averaging around 6 km/h. I don't recall what pads were on this bike.
Other time was in a road bike race, at -10.3% average gradient with 503 metres of descent in 6 minutes and averaging ~55 km/h. I could smell my brake pads and feel the drop in performance. With a hard turn at the bottom I was evaluating my bailout options, including a foot drag and a complete drop on one side. Fortunately I managed to drop my speed enough to make the turn using the whole width of the roads - hooray for closed-courses! This was on stock black Shimano brake pads, normally perfectly adequate.