Mechanically linking is heavier than fbw/electrical/fiber optic linking, and what's the point if there's no mechanical linkage to the control surfaces?

With the fbw system, the software makes the choice on how to interpret the control movement, use one or both? If one, which one?

EDIT: Maybe you mean that a mechanical linkage would provide a feedback mechanism, so that one pilot would know if the other pilot was attempting an input? I don't know if there's force feedback on Airbus flight controls.