DozyWannabe dared writing :
the rudder barely came into it
Read the report in full, including page 1xx where you will find the rudder traces. Just because BEA did not expand on the subject does not mean it is irrelevant.
You yourself have used the expression PIO (which stands for Pilot Induced Oscillation). Experts now prefer APC event (Aircraft Pilot Coupling), which better emphasizes the interface issue. There is a definite APC event in this instance, in roll and yaw. Rudder played a huge part, as a fast-moving, oscillating control surface with zero feedback to the pilots.
Regardless of what actually caused these oscillations, and why did PF had such trouble keeping the ship's wings level, rudder certainly played a major part in the whole sequence.
That the system governing this particular control surface was subjected to a large update is in itself source of questioning.
Yes, looking at the traces is dull work. But as long as we take these recorders for the truth of the matter, the traces are all we have as unbiased data, along with the ACARS messages. Unless one is prepared to use and study them carefully, one can only follow pre-made conclusions written under careful supervision by interested parties. Such should not satisfy an inquiring mind.