I don't think this is correct, you actually want a design that has high cogging torque when the motor is running, this is what makes an easy path for the flux to complete its loop. Like others have said typically I^2R losses are the largest proportion, so anything you can do to lower current (i.e. by using stronger magnets) will be good. Also for direct drive hub motors (very low frequency compared to high-speed machines) I would not expect hysteresis to be a large portion of losses, but this depends on the steel and I don't have numbers on this.