still, the one used on those very light bikes, like my Woosh Faro, is the Aikema G85R which weighs only 1.7kgs. There is not a huge amount of magnets inside the motor.
When you compare hill climbing performance with its larger siblings:
G85R: 40NM max, 1:12.6 reduction ratio, 1.7kgs
G100R: 40NM...