But DW,
I would argue that, though perfection is unattainable, all engineering and all art strives to get as close to perfection as possible. "It's good enough" isn't good enough in the case of airliner design, IMO.
If the side-stick or yolk could have been seen by the other pilots, there would have been perhaps a better chance that somebody would have figured out what was wrong. Not to say that's what caused the crash. I dunno about you, but when I get on an airliner, I'm hoping that I have every possible chance to live through the experience.
Not sure why you (apparently) see no room for improvement in the AB interface. Not meaning to challenge you.