Just got back home after driving through WW1 battle areas, so I am going to stick my head above the parapet and duck back quickly!
I'm not at all convinced that it is fair to describe the lateral oscillations immediately following the AP drop out as being a PIO, although I can see why people should describe them as such. PIOs, technically speaking, have control inputs out of phase with the necessary corrective actions and the bank angle excursions should be increasing, not falling.
I think the point being missed in the discussions of 'sensitivity' and 'startle' is that there was a fundamental change in the piloting dynamics when the FCS reverted to direct law. IIRC in normal and Alt laws a sidestick movement commands a roll rate, but in direct law sidestick commands roll acceleration as in most aircraft.
Now I am not a pilot, but what I learned in studies of several aircraft is that to get stability the necessary control techniques are very different in the two cases.
What I see in AF447 is a pilot struggling to come to terms with an unfamiliar control dynamic; OK, it is one he had seen before throughout his early career and training, but not one which he had used recently. The (damped) oscillations result from his re-learning process and personally, I think he made a pretty good fist of it. I can't see them as a fault on his part, which describing the motion as a PIO somehow implies.