I Still think the motor plays a large part. Its not just about the stored energy. Take a stupid example where you have a 500mm disc with a tip speed of 100mph and only weights 1 gram. If you have a big enough motor (with no MOI) to maintain this speed and produces a torque of 500Nm then if Ive done my sums correcty you will have a point impact force of 100kG @ 100mph.

Dont all shout about it its probably wrong and completely ignores the stored energy in the disc as it does not weigh anything.