"At what point does a demonstrated lack of professionalism in a complex operating environment override any other relevant components of the accident."
Never as the reason for the accident was the DC10 strip on the runway,see the posts of AlphaZuluRomeo and DozyWannabe who both clearly explain how without that piece of metal the accident wouldn't have happened.
That doesn't mean that a "demonstrated lack of professionalism" if proved shouldn't be addressed.
The difference of opinion highlighted in many of the previous post is in my view caused by trying to prove that "a demonstrated lack of professionalism" trumps the DC10 strip on the runway.