I'm not an expert - but the axial flux design while old is been largely ignored due to manufacturing problems that have now been overcome ( so most of the dev has been on the radial flux variety ).

And apparently axial flux motors have shorter magnetic flux paths which reduces losses.

ie the efficiency gain is due to the switch from radial to axial flux - not some incremental gain on radial flux.

Having said that the efficiency gains are relatively small - 1-2%.

However again there is a compounding effect, in that the reduction of loss of energy as heat, leads to requiring less cooling - and/or the motor is able to operate a full efficiency over a wider power output range ( as heating the copper increases the electrical resistance ).

https://www.stanfordmagnets.com/advantages-and-disadvantages...