The two things that seem to big huge contributors to the crash are that the pilots may not have realized they were in alternate law soon enough & one or both pilots did not realize that one of them was holing the stick back stalling the plane.Both of these seem like glaring UX & training issues.

It does not appear that it's very clear when the plane goes into alternate law & it does not appear they receive much training on how to fly in alternate law. Even if they do receive training, you probably do not want your most novice pilot handling the controls in alternate law. Additionally the averaging of the inputs seems to be the most obtuse way for pilots to realize mismatched inputs.

I agree with you in general that it is a balancing act, but if you're going to have a modal interface (normal law, alternate law) and the plane's flight controls are going to perform differently depending upon that mode, an indicator of which mode you're in is immensely important in any situation.