"Difficulty in determining what the other pilot is doing with the stick is a factor of the design, sure - but that's a known thing, and given the safety stats, it has not proven detrimental to safe operation of the aircraft "
This is correct and was discussed in detail in the book "Understanding Air France 447", by Bill Palmer, who was an A330 Check Airman for nine years.
The moment both pilots give sidestick commands, a synthetic voice loudly and repeatedly announces "Dual Input", and a light in front of each pilot flashes. There is both audible and visual indication of conflicting commands.
I worked at an airport where a student pilot stalled a light plane and refused to release full back pressure, no matter how loudly the the instructor shouted. This was similar to AF447. Finally the instructor struck the student with such force it broke several ribs and he finally released the controls. The instructor recovered the aircraft so low the landing gear was broken, but they both survived.
When total mental confusion and panic takes over, it can make little difference whether the indication of control conflict is audible, visual or tactile.
Bill Palmer analyzes several cases where similar situations happened in Boeing aircraft, and the conventional control system did not prevent an accident. It's not a pro-Airbus book, but analytically and impartially studies all data related to AF447.