Power numbers may be off, they may not be off.
Powermeter manufactures claim 1 to 2% accuracy. 2% accuracy doesn’t mean they are always 2% wrong, but should never be more than 2% off. Also, the accuracy of power meters is as much an argument pro doping as it is against (as they might be over reading or under reading, who knows?)
Climbing speed and eye test (the latter is by no means scientific, but probably the best way to get a hunch of who might be on the Capri Sun) fit the power numbers that were reported. Also, the numbers from Van der Poel are even reported by his own team staff, so I guess they fit in line with what he has proven to be capable of time and time again in training and racing.