I also beleive that this red thingy doesn't do anything.

"am", i don't thing anyone can tell a difference from this change on the track...we barely see the difference between two different top engines at this point,imagine trying to see a very small difference between the two cranks.
No-way!!!

The mass that is removed is in the center of the whole rotational masses so the effect is even lower.
The biggest difference would be between a flywheel of 40mm diameter and one of 30mm diameter.
In this case you have less mass away from the center and this lowers the total rotational mass more.