Mate, comparing the effectiveness of a lightened flywheel is far more complicated than the equations you have pointed out. There are many factors such as gear/diff ratio which amplify the load reduction on the engine during acceleration. Highest improvements in acceleration is in the lower gears and less effective within the higher ones. Depending on the engine, g/box, diff etc, you can reduce the effective weight of your car significantly (in first-second gear). Without going into the details which requires some serious calcs, let me assure you that you will definitely notice the difference of a lightweight flywheel.
Mind you it does have draw-backs.
Cheers,