AnFI - trying to come back to the original proposition and why I feel uncomfortable with the simplification, or in your terms whether the baby is being thrown as well as the bathwater. I'll try and sum it up in words, there will be inexactitudes in wording.
To calculate the moment of inertia you integrate the masses at each position. A hoola hoop has a different "inertia" to a disc of the same size and weight. It is reasonable to assume that in most cases the mass distribution along the blade doesn't change with rotor speed. For lift you have to do the same. So the real question is do you think that lift distribution along the blade is constant with rotor speed?