Paul - a very informed and interesting post - you have clearly been there, seen that and got the T shirt as far as Robbie flying is concerned
The quoted rate of roll from the TR thrust is rather sobering - and that was from the bloke who designed it - wonder if he ever thought there was a better way?
I still believe that at zero G in a teetering head helo, you can wave the cyclic as much as you like but, whilst you are changing the disc attitude, the rotor has no effect on the fuselage attitude until some positive G is restored - in the case of your 90 nose down, the fact that you started to accelerate towards the ground restored the G which allowed your aft cyclic to take effect.
The rotor head has to pull the fuselage around the sky on a teetering head helo which requires the weight of the fuselage to be pulling down on the rotor - this can't happen at zero G.
I may be wrong about my suggestion to use collective but it makes sense from the physics.