Remco is saying these things because downhill is his weak point. I think he is a rider who would be very happy if stages were only flat/rolling/uphill.
I haven't got any stats to hand but i think there has been an equal number of death/disability, from crashes or getting wiped out by cars/motorbikes, in pro cycling on flattish terrain as on alpine descents over quite a few decades. There have been a few heart attacks, too.
Actually; if i think about it i think there might have been as many deaths and disabilities from crashes on velodromes, in the same time period. Regarding velodromes; if you go back to the days of Major Taylor, when motor pacing on the track was a big thing, velodromes might actually top the list. They had some god awful accidents back then with all the steam powered motorbikes and tandem/quad pacing events. Spectators dying or getting maimed, too.
Training still worst for bad outcomes, by a long stretch, and that seems more likely to happen at the roundabout a few hundred meters from home than on a mountain 100 miles away.