I've just been reading about Hannah Gutierrez-Reed, and there are a lot of red flags there. It was her second job as lead armourer, but the crew from the film during her first job reported several extremely concerning incidents: firing the gun without warning, reloading it on the ground near debris and pebbles without then checking the barrel, etc.
Plus, she had put a number of pictures up of herself holding guns in quote-unquote "cool" poses, which just gives the impression she didn't afford the job the proper level of seriousness.
I get that vetting and hiring makes the producer liable for the mistakes of their appointees. I can see Baldwin being responsible for that. But the actual firing of the gun, not so much: he had been informed by two separate professionals that it was not loaded. Manslaughter doesn't seem appropriate for that. Something related to improper vetting or negligence maybe, relating to the hiring process, but not manslaughter surely.