I asked Jeroen Swart this during the "Power training" articles a few years back when training remains HR based for Pro's. Unfortunately I didn't get the answer I was looking for. I am sure at a certain point elite and pro cyclist reach their maximum fitness according to their heart rates and only their rest and general health influence their HR based metrics. Except the obvious 'skills and handling factor', how will someone differentiate their HR based training from Nino Schurter if they both perform a 20 min session @ 90% Max HR? I feel power becomes the metric to use. So realistically, no matter how much skills, bike-handling and even luck plays part, your 20 min and 3 min FTP will define your position in a race.