I'm not so sure that assumption can be made - yes it's published that other hubs have a ~0.2 W loss for bearings, but the fact that the charts discussing SA X-fdd show same resistance regardless of the presence of electrical load or not forces one to also consider all non-electrical components of the system.

It would be interesting to pull of the drum pads and repeat the test, but of course it is not so easy to do a loaded bearing proper test for these. Schmidt has a complicated apparatus to test this.