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@gbj_tester
O level physics, it's more than enough. He's casting aspersions based on what he suggests (not knows) is a credibility gap of around 2% based on his calculation of power output. We all have a pretty good idea of what you need to know in order to relate power to cycling speed, but for anybody new here's a list:
Rider mass - he's guessing, not measuring
Equipment mass - he's guessing, not measuring
Rider+bike CdA - he's guessing, not measuring
Tyre Crr - he's guessing, not measuring
Distance travelled - he's guessing, the TdF road book isn't a highly accurate measurement although it's probably better now than it was in the historical period he uses for comparison, since GPS became ubiquitous.
Duration - he's using TV pictures, presumably, rather than stationing an approved timekeeper at a precisely surveyed start point
Elevation gain - he's guessing, although there's pretty good public domain topographical data
Air pressure/temperature/humidity/wind speed - he's guessing, not measuring. In fact, nobody even could measure that stuff on a mountain ascent, it varies so much both temporally and spatially. It's hard enough to get that stuff nailed down in a sealed velodrome.
On the physiology side, he's guessing VO2max, gross efficiency and the ability of outliers on the athletic spectrum to maintain high proportions of maximal effort over given durations. Pretty much by definition, champion athletes have surprising abilities to physiologists used to looking at data from less elite populations.
As an analytical method, it's only slightly better than a Fermi Estimate. Sure, do the maths, and if somebody is doing 9W/kg by your estimate then it's likely that there's a problem, but when proper science says 98 and your Fermi Estimate is 100, congratulate yourself on waving your arms in roughly the right direction but don't cast aspersions on people when you have essentially zero evidence.