I don't think there are any losses on a (reasonably short, i.e. without intermediate supports) axle transmission, the only form of attrition are bearings and on

I don't think there are any losses on a (reasonably short, i.e. without intermediate supports) axle transmission, the only form of attrition are bearings and on both sides of such a setup you need one anyway, unless the same bearing is common between the wheel hub and the motor (i.e. the motor is actually the hub).