Regarding #6...Boeing charged $80k to unlock the software feature to gather data from more than 1 angle of attack sensor.
80k for a _light_ in the panel, not to have MCAS take the two sensors into account - which it couldn't do anyway. With two sensors, how do you know which one is right and which one is faulty?
The developer fails to check for an error condition or raise an exception because doing so would add too much complexity to the system. So instead it is assumed (or hoped) that it simply can't or won't happen. Problem solved...
(Edit: Or that the user will just have to reboot if it happens.)
Probably AA or SWA demanded it, and Boeing compromised by charging for it.
But... #6 was about paying attention to the other computer, not the other sensor. That would involve some big and expensive changes to the flight computer software, which they probably should have done long before the MAX project started.
More management failure.