It is not "that simple".
We have 100 years of "action movies" in which actors point firearms at other people and pretend to shoot them. It is an inherently dangerous activity, and the film industry has developed elaborate safety rules to prevent injuries or deaths during this activity. Those rules work - when they are followed.
They weren't followed on the set of Rust. There was a long chain of failures by multiple people that lead to a fatal outcome.
The "79 rules" of "Industry Safety Bulletin #1" have a much better record than the "4 Rules of Gun Safety".
In that context, Baldwin was third in line for at-fault behavior, well behind the gross negligence of the Assistant Director and the Armorer.
Whether New Mexico law will consider any of that is an open question. That is what expensive defense lawyers are for.
Good point about the actual governing safety bulletin. Here it is:
https://www.csatf.org/wp-content/uploads/2018/05/01FIREARMS.pdf
One thing that I think will come out at trial is the the armorer (working for the Property Master) was an apprentice or newly trained young woman. As Producer and/or in-charge on the set, Baldwin had previously dismissed her from her duties as he disliked her input. She was not involved in the fatal encounter.
My suspicion is that he was allowing firearm extracurricular activities and she was upset. A live round from staff horseplay usage was left in the weapon and bone head Baldwin had the trigger depressed as he was making out his acting.
You can make it as complicated as you wish, but what I said still stands.
The final user, in this case Baldwin, is the one responsible, both morally, and legally.
Others may have contributed to the negligence, but Baldwin shot the two people. It’s that simple.