[Reeses]

I stand corrected, electric current uses the whole wire. Layman books can be just as wrong as the internet.

Hollow wire cooling does seem to be a workable idea, allowing 50% smaller motors: DEF_Internally_Cooled_Hollow_Wires_ATZ-2017.pdf

[RFEngineer]

You’re not totally incorrect (center of a cable is not significant at high frequencies), but at DC, 60Hz AC the whole wire is used.