Chug,
You say that the situation would be the same under a unity authority.
No, I don't think I miss the point. Firstly, the MOD is not obliged, under law, to promulgate Safety Cases. However, because it is a good idea, we have done so. Unfortunately, the individuals involved this catalogue of errors, got it so wrong in the case of Zone 617. It doesn't matter how you dress it up, but human error in any single organisation (CAA?) is still human error. That same person would make the same mistake if he/she was working for RAF/MOD/QQ/BAe/CAA or Fred Carnos Flying Circus.
The creation of a single MAA does not stop human errors.
The NSC was not flawed in its structure which, I am confident, would mirror any structure imposed by any suggested MAA. The NSC was flawed in its judgement, which was based on poor information supplied to it. So, if the supplier of the information (BAe or IPT) is going to be the same organisation, regardless of the who does the analysis, the judgement is doomed to fail.