"When the helicopter executed the steeply banked turn to the left at low forward airspeed, the inertia in the main rotor blades and main rotor RPM would have decreased, resulting in less main rotor efficiency..."
Think you may have to be gullible gulliBell to swallow that one in my opinion. Ask yourself "does the rotor droop when in a turn, no matter how steep?". Question 2. Under what conditions of powered flight does the rotor droop? Simple question me thinks. Governors in the main do a bloody good job and quickly regain any transient droop from a sudden application of power, providing you don't top out of course. Inertia in the main blades???? Can see where they may have come up with this argument, but the effect would be minimal and theoretically getting some what esoteric (fuselage begins turning in the same direction as rotor rotation so the rotor has to speed up in effect to maintain the same RPM with respect to its point of reference, the fuselage)