Terminal balistics is a knowledge category. I'd expect Dr. Fackler to have far more knowledge about that than pretty much anyone who uses a gun in combat. I also wouldn't expect him to be much use in delivering situational skill training about how to handle a gun in combat unless he has done so repeatedly, or had some experience and worked with others with experience to develop a coherent model of how that chaos works.
Similarly, I can pass along some information about the psychology and neuropsychology of threat situations. I can even talk about things that are likely not to work (based on what we know from research). That's knowledge. My personal experience with threat situations is not sufficient, IMO, to realistically teach de-escalation. I've done it on rare occasions, and have no idea what part of what I did was important, because I have too little data to base it on. And since I have so little experience dealing with those situations, I absolutely would not be qualified to lead any kind of situational role-play about de-escalation, no matter how much I read and learn about the context.
This is what I was trying to get at about there being some topics I can teach about. I have a lot of knowledge, and I can even pass along some of the information I learned from others with experience in threat situations (I trained with several cops, bouncers, etc., and taught a few). But no matter how much I read and am trained by someone, I don't think it would be a good idea to have me teaching how to handle firearm combat, for instance, since I've never been in that situation. I could teach some techniques that could work in a retention situation, and I can teach gun safety and target shooting (have done, in fact), and could even teach a bit about SD law in respect to firearms. But not combat in that context.