It’s true that, if the gun procedures are followed, they work. But there’s an argument that you need to prepare for them not being followed. While this particular example was particularly egregious, I would like to see how well gun procedures get followed on sets, particularly the lower budget productions where there is an impetus to cut corners. Just because no one has been shot doesn’t mean that they weren’t being really unsafe. From there other ideas could be implemented.
One I wonder about is using color to help distinguish the real thing from the fakes. Color grading is pretty cheap these days. So it could look more or less accurate on screen.
I do also wonder if the realism requirements with other things are as big as with guns. I know that, as a former music major, I got used to people not really playing instruments in films, without it pulling me out. Computers often are unrealistic to better communicate the plot. It seems to me that you can get used to things not needing to be accurate as long as they convey the right idea (like the ideas above about how bad violence is).
I still think a lot of suspension of disbelief breaking is due to not being used to things and not expecting them. If you expect the level of accuracy that you get, then it’s not a problem. It’s the surprise that pulls you out of the moment unwillingly.
(That said, I do love analyzing them just for fun, too. I just do that during a lull in the story or on a second viewing.)