I think the key to being a good cycling commentator is knowing when to fill air, and when to commentate the race. Sometimes that involves basically interrupting yourself!
"And here we see this castle, where - in 1258... there is an attack from Movistar!"
Absolutely. That is probably something that can only be learnt through years of experience. In Germany there is a female commentator for football who suddenly commented on big games and there was a huge debate whether she was good. Lots of people hated on her (voice not good, bla bla bla, though she has a good voice) and lots defended her (she knows much better than the male collegues, you just hate her because she's a woman). I hated to have her as a commentator, too, although everything she said was totally true, she obviously knew what she was talking about. But she just talked and talked... and when there was a goal scene she'd talk about Neymar's transfer... That became a lot better with time! But it made me realise how important it is to "lead the spectator through the events", instead to just give information.