thf:
Before the stall: The biggest puzzle, in my opinion, is Robert. He did notice that Bonin was behaving erratically. But he didn't follow up on that thoroughly enough. Why not? Langewiesche has the idea that, when Bonin took away his control immediately after Robert took over, Robert didn't notice this and wondered why his sidestick didn't work. Maybe that is a clue: Did he think his machine was uncontrollable even before it really was? If you want to question unconnected sidesticks, I think that would be the moment.
You are addressing a bedrock CRM issue: one pilot flies, the other monitors/assists. If they were, in Airbus fashion, "fighting over the controls" ... either the controls "sum" the conflicts or the "take command" function returns to Bonin (per how AB designed the interaction between the two side sticks), then your point on Robert being cut out of the loop (and hence calling the Captain?) goes to the heart of a CRM and cockpit gradient issue far more than a flight control style issue. (That, and at least one instrument scan that was broken/behind).
More troubling for AF than for Airbus, in some ways.
The further mess of going so far into stall that stall warning was disabled (AB design feature), lack of an AoA gage (done to death back in the original threads) and the return of a stall warning when AoA was again alive ... if they even acknowledged stall warning as other than spurious ... combined with the most recent "condition/response" training for approach to stall being the "down low/near the ground" scenario ... puts a lot of conflicting and non-normal things saturating the crew's awareness at the same time in a scenario I doubt either had seen in a sim.
Small wonder that at least one of them was confused.
Captain Dubois had quite a bit to clean up and sort out when he arrived on the flight deck and tried to figure out what these two had done to his plane when he left them alone together, in cruise, straight and level, a short while before that.