Obviously the system should improve to make errors less likely, but that doesn't absolve anyone of guilt in my view.
in this case, the backup driver should shoulder some blame, but not the majority of it, and commensurately, should not face any of the harsh penalties associated with manslaughter.
the wet bags behind the autopilot get bored, distracted, complacent, ill or reckless due a moltitude of factors some of which outside their control
it is well known at this point the human modes of failure, and that there was basically no mitigation is a reasonability of the system designer
A better system would have spotted this person was watching their phone not the road, but it would still have held them accountable and (at minimum) fired them!
That doesn't mean that an employee being clearly negligent doesn't also need to be held accountable.
Them being held accountable is one part of a good system.