PILOT ERROR cause the A447 accident - nothing more, nothing less.
I dont think anyone disagrees with you. It is pretty clear the accident was due to pilot error. The comments advocating linked sidesticks are about reducing the posibilty of similar accidents by making the controls less susceptable to pilot error, less susceptable to training deficiencies, less susceptable to failures, such a pitot tube blocking, causing confusion etc.
Even in a "perfectly good and safe design" there is always room for improvement.