Dozy, I totally agree with your analysis of Bonin's mental state, except you really do not understand the reason for Bonin's mental state. That was a direct result of the PIO.
Bonin was startled by the AP disconnect, yes, but that was not what sent him into PIO land. His past bad flying habits caught up with him. He did not initially appreciate that he was no longer in Normal law, however he made control inputs that were unexceptional (to him) and had the aircraft react in an entirely unexpected manner. From that point on, he was mentally fighting for his life. That is the effect of PIO on the pilot flying, and you might call that a startling result, but it was not the result of startlement.
If BEA had personnel with PIO experience on the team, they should have made that connection, but that is not the direction they took, ergo, they were not able to properly cover that base IMO. This is not to cast doubts upon their work however. It seems that hands-on PIO experience is very rare.
I am not sure Bonin actually adapted to the new AF447 flying characteristics. It is equally possible that as the aircraft slowed and Q decreased, the aircraft's response began to match his mental model and he was finally able to stabilize the roll oscillation.