A few things made it not fun -
The slope, extended duration of the descent, and repeated hairpins that limited how much speed I was comfortable carrying through turns all made it very difficult - to the point that I was stopping regularly to ensure I let the rims cool, and by end of day, my hands were pretty tired. I am around 165 lbs. for what it’s worth. I was using GP5000TL - so no risk about tube failure, but still, I felt I had to be a lot more cautious than I would have on alloy wheels. Also, it was dry - if it was wet, I can’t imagine how bad it would have been. Wheels are recent reynolds assaults with their required blue cryostop pads. Maybe higher end might be better, but these aren’t no-name or out of date wheels.
A bike rental shop I used in the past also mentioned they stopped renting with carbon rim brakes this year after having quite a few rims fail last season due to extreme heat on the braking. A giant shop, so all tubeless - they weren’t tube failures, but rim failures. I can absolutely imagine overweight and inexperienced cyclo-tourists absolutely demolishing wheels/brakes riding down that kind of terrain.
But again - I’m talking about it being a problem specifically for descending hairpin HC climbs in the Alps… for most all other uses, I’ve been really happy with them. Outside of the hairpin sections, I found they were fine on most of the other stuff I rode over the month. So I will still ride them 90% of the time here in NY - but will bring a pair of alloys next time I take my bike to France
Also, agree that the wet braking issue is normally not a huge deal other than the delay. But I really wouldn’t have wanted anything more working against me on those alpine descents than I already had.