Since everyone wants to continue this thread......

There are two “givens” with a light weight flywheel. The reduced mass makes it harder to launch the car, and the reduced mass eats up less power when it is being accelerated. For road racing and auto-x, where the vehicle only gets launched once and then has to deal with repeated accel, decel, shifting, the lighter flywheel is a clear advantage.

For drag racing, it's not so clear. Sitting at the line, bringing the revs up in neutral stores energy in the flywheel. Drop the clutch and that energy helps propel the car forward, resulting in reduced 60-foot times. Shaving 1/10th off the 60-foot time can result in a reduction of 1.5X to 2X that 1/10th at the end of the track. But the issue is whether that reduction offsets the loss of acceleration due to the energy absorbed by the flywheel, bringing up to higher RPM while traveling down the track. The answer is not clear, and most likely specific to things like weight of the vehicle, the engine's torque curve, shift points, etc.