1. Yes
2. Yes
3. No. But there's darned little "scientific data" about cycling. Everyone is different, thank god, and we all have different goals and histories.

Personally, I believe in the Decline of the Great Dark. My fitness falls off in winter and there doesn't seem to be a darn thing I can do about it.

Peak fitness does not result from overtraining, however overtraining can result from futilely attempting to maintain peak fitness. All those pros are probably not wrong. It's a glandular thing, IMHO. High glandular output is unsustainable.