An acquaintance of mine offers training services to state LE and likes to make a point about that: We like to think that police are experts at firearms, but in actuality, a civilian trainer who specializes in the topic is usually far better informed. Police have a lot on their plate, after all, and firearms skills are just one of those.

I did training prior to deployment overseas into a conflict zone, and benefited from instructors who had already been over there and seen some of the worse it had to offer. I could see that an instructor who both specialized in a topic and had outlier experience within it as being ideal. You could even just say it's actual experience, the reality-checking of theory, no different from how you might benefit learning software dev from a prof who had been a SE at some point. It's the difference between learning from someone who's only read about a topic in books vs. actually done the thing. Kinetic combat (like software development) is one of those topics that the actual reality diverges from media depictions, so that grounding in the real is why you train for it in the first place.

Neutralizing threats in an intense situation requires split-second decision-making. These decisions will be scrutinized after the fact, possibly for years, so the purpose of such training is largely to hardwire the correct action into reflex.