The power data JOIN imports from Strava are not the average power or the weighted power but Strava's calculation of "Normalized power". Normalized power is the average power but without the zero's, so basically it is the average power you were producing over the whole ride but with the stretches you were freewheeling (and thus pushing 0 W, like on a downhill) taken out.
My Strava power data are different from JOIN's.
