212Man:
You are always a precise and well informed commentator! I take your points exactly. I'd just like to amplify my point, though.
Going back to the SA330, there is no N2 indicator so it is impossible to tell, with the engine running, whether or not there is sufficient residual thrust at 'idle' to prevent the freewheel being fully disengaged. The same is true for any other helo with no N2 indication, unless it has a centrifugal clutch such as on the Astazou and Artouste engines.
If the freewheel is not fully disengaged, the engine's residual thrust will provide a small power contribution, offloading the aerodynamic effort required to keep the rotor and gearbox train turning. For the SA330 Puma (one last time!) there is hard data to show that the engines make a power contribution in (flight/ground idle glide) autorotation.
On a piston-engined aircraft, the split between ERPM and RRPM will indicate whether the freewheel unit has functioned and the engine is not assisting. For turbine engines, it is the N2 / NR split which is vital to show the true status of the autorotation.
(One last point: the Super Puma AS332 has a different, though similar, power train to the SA330: but with N2 indications.)