Now wait a minute. The only time you'll loose anything is when you let go of the gas. Think about it.
If a flywheel is heavy it's going to slow down the motor when you hit the gas. If it's lighter it'll respond faster to the throttle being hit.
Now, if a flywheel is heavy it will "push" you a little more when you let go of the gas. If it's lighter, it will rev down faster.... This is the only loss.
Most people will add weight to gain tractability (Slow the motor down when you first hit the throttle so the tires don't break free).
The motor produces the torque... not the flywheel. If anything, you'll add torque when on the gas and loose some when you let off the gas. Who needs torque when you let go of the gas.
Now, on the banshee, it takes time for the motor to pickup then it's off. We banshee owners want it to kick in sooner most of the time. This is a way to do it.
A lot of 4 stroke owners like to add weight so it slows the motor down when they first hit the gas. After that, the flywheels mostly out of the picture anyway.
This is how I see it anyway