Let's be specific. 447 shows us some very pertinent data. The SS is the heart of the life and death of this flight, agree? For three years, this thread has made abundantly clear that the two pilots were not a team, and PF tells, "I have been pulling back for some while"....
Inarguable. So let's look a bit further. The very device that could have saved the flight, did it in.
Moving the controls apart in the cockpit, from the front to the side, ISOLATED each stick from the other. (See Lufthansa, Tip Strike), To the extent that the Stick cannot be recognized by the partner/Pilot, sufficient to show the command, the aircraft is operating SINGLE PILOT. This is unacceptable. As jcjeant and CONFiture show, a belated display to show controls results is not best practice.
Explain, apologize, distract, insult, the truth cannot be hidden. Part of the direct cause of the crash involved a lack of proper brief of the Captain. When told to "Climb", PF says "I have been...." A critical and obvious 'brief' is the position of the controls, stop. It also requires no time to discuss, if visible to others.
I submit and suggest that the confusion that developed in the cockpit had more to do with the lack of visibility of the SS's than any other factor. And Confusion in the teeth of surprise is, obviously, in this case, Fatal......