RWA,
I don't know you're experience but you are one of few posters here asking the right questions.
In the Perpignan Accident the autopilot was disconnected in level flight and the aeroplane decelerated. The pilot would require to applying increasing nose up attitude to maintain level flight. The auto-trim would react correspondingly.
I see your point about the pitch down inputs made by the Air France F/O. I personally believe that these were token gestures to reduce the rate of climb. If the aeroplane has reached a pitch attitude of 10 degrees nose up then the trim would be wound back. The fact that the trim wound all the way back does, in my opinion imply that the F/O's inputs were predominately nose-up and as I say his inputs would have to be sufficient to allow this to happen. I don't think for one second that the THS acted alone or there was a failure.
What it would have amounted to, in aviation terms, is that the 'systems' should have reverted to neutral settings after they signed off - so that the autotrim, for example, would not have just signed off and left the THS at an unheard-of 13 degrees up or so, but would have reduced the angle to a conventional setting (say 3 degrees up or so).
I completely agree and a very valid point. I believe that in both accidents both crews failed to appreciate that auto-trim was no longer available and it was necessary for them to move the trim wheel.
In my opinion and from all that I have read, the aeroplane responded as it was designed to do in accordance with the pilot inputs that were made.
Why he made those inputs are yet to be explained.