As someone who has NO industry axe to grind, I strongly believe that ALL of the above were dangerous holes in the Swiss cheese, and if any one of the above factors had been not present, the crash might not have happened.
Yet another way of looking at it is;
With so many barriers present (layers of cheese) it would be extremely improbable that all, or enough of them would fail resulting in an accident.
Obviously some of these were not actual barriers but intead were latent failures already in place (holes drilled in a line though multiple layers of cheese) because nobody had bothered to validate some of these barriers as being effective much of the time.
My strong convictions are that we can't expect all layers to work all the time, but that we must demand that controls and evaluations are in place to at least qualify that a layer of defense is active and not a dream on a piece of paper assuming that the other guy has it covered.
That's why we have regulators, to make sure that the process is active