You're clearly missing the point regarding tyre traction. Once it goes it goes. Doesn't matter whether it goes under caliper, cantilever, v brake or disc, there's only so much braking force a bike can handle before the bike either flips or skids.
Night and day? Really? Rubbish.
Rims don't need to be 'dead true'. They can be anywhere up to about half an inch out of true and still be braked safely on. The same can be said of disc rotors. They can be an absolute nightmare to straighten once bent and without specialist tools, are near impossible to get true again.
Alot of the mess from rim brakes is due to the larger area of their braking surface. Disc brakes also leave residue in wet conditions but because of their smaller diameter it doesn't create as much. Both can be easily cleaned.
Rim failure through wear on long distance and rtw tours isn't at epidemic levels. In many cases, a replaceable rim can be easier to find than a warped disc rotor or worn pads.
I think you are missing his point, heavily laden down a 25% mountain pass, it’s not a lacking of grip that is the issue, it’s the build up of heat of the braking surfaces, whether rims or discs, one is better able to cope with heat than the other, and you can safely use them more,
It’s easier to straighten discs than replace rims, done it many times with just an adjustable spanner, on mountain bikes, I don’t know why one would be looking for a warped disc rotor, and pads are easy to bring with you, your much more likely to know when pads need replaced, than when rims need replaced,
My tourer has disc brakes, but retains cantilever mounts as a back up, the wheels being suitable for both, I actually don’t mind using either type, but commuting in all weathers I would prefer discs, especially if a small wheel bike like a Brompton, which wears rear rims fast If using all weathers.
