My guess, I'm quite confident Evans and Basso are good examples. They chose not to have doctors has helpers but a well and internationally known trainer, Aldo Sassi, that's universally recognized as a firm and strong anti-dopers. Moreover, BAsso is putting online practically every medical value about his body, and everybody can access it (I did this morning and they are very precise and complete) .
I don't know in the past if they cheated (Basso of course yes, Evans no idea), but Sassi stated that Evans is the most powerful rider he had ever trained, and Basso plays his league, too.In the history of cycling there have always been very superclass riders, and probably those are among them.
I'll add present Cunego and Gendermann, and even current Valverde (he's so targeted he wouldn't dare, I believe) but of course he was so full during his kelme and illes balears days that he may be still under effects right now.