Lots of big hills in Colorado. Really big. Trails with over 2000 ft of vertical, mud puddles, 3 ft drops and ginormous rocks all over the place. Brake fade is life threatening on those kinds of rides. So is snapping a brake cable in the middle of long descents, which has happened to me with rim brakes on more than one occasion.
I’m a big guy who abuses wheels. Having ridden thousands of miles on disk-brake equipped bikes in about the most demanding conditions imaginable, I feel qualified to say without a doubt it was underbuilt wheels or shoddy assembly rather than the disk brakes that were the problem.
I had much more problems with wheels staying true with rim brakes. The wheels required weekly truing to keep them from falling apart. Wore completely through both rims on my trek 930 in under a year when I was commuting 100+ miles a week. I’ve never had to touch the wheels more than once/twice a year on my disk bikes, and only after doing things on them that most people wouldn’t do on a bicycle.
Well, you put THAT in perspective. I only biked around Colorado Springs, never the big mountains.