But wait, what actually happened here?
Back in happier times it was deemed necessary to fit the LEAP engines to be competitive. It was also deemed too costly to house longer legs. However, moving the engines forward and up a tad was not all bad, the new thrust didn't have quite the rotation leverage of the NG. Good, but then came the handling on the approach to certain types of stall. Not so good. In fact, the aircraft wasn't certifiable without a fix.
The aircraft already had a black box that 'adjusted' the most powerful control surface on the aircraft. It had worked well for years so why not just write a new algorithm to overcome the light control feel that's a no-no? Seems pretty sensible when you consider what we've just saved - the final sum being part of an Airbus-advantage subduing equation. That is a lot of High-$ reasons to take this course of action. But then somewhere, someone . . . possibly just one person, allows the input from just one AoA vane to be a prime messenger to the system. They, or another someone, deems the g input unnecessary.
Despite there having been a lot of deeming going on, at this point in time it's not as logically bad as one might think. The vane is NOT deemed an item that is in the 'catastrophic' category and so it really wasn't vital to fit a third vane, or even design a comparator circuit to reject unlikely AoA signals and swap to the other one in the blink of an eye. Plenty of data to make a reasonable choice.
In some obscure office, someone deemed the rear Column switch to be in need of rewiring. It's just possible that in the very next office, a person altered the cutout switches on the centre consul. Not one aviation analyst in the world seems to know why they did that.
Nothing in the above is too far removed from things I've read about in the last 55 years. Not that unusual . . . until two vanes fail within a few months because of totally unrelated issues - that is incredibly bad luck, not giving quite enough time to get the significance of a 'Catastrophic' category awarded to those components in time for the second catastrophe.
Strings of events, or holes in cheese, this run of events will change the world's aviation industry forever. You may think it will be like the DC10 or the rudder hard-over issues, but it's so different, in so many ways. There is such a tangled web that it will take not just decades to be 'forgotten', but generations, yet looking at the logic lines, few of them haven't got uncomfortably similar history, it's just the relentless addition of those holes that caused the final disasters.