Agreed on that last point. But "knowing something about" self-defense doesn't require hundreds of personal encounters. If if did, nobody who didn't have them would be able to deliver anything effective for that context, and you and agree that MMA training is one effective preparation for that context. Training people for self-defense requires an understanding of attacks, perhaps a touch of psychology (especially physiological), and some skill in a system that provides techniques that will work against those attacks. Validation of that effectiveness should come from a range of sources, including hard sparring/randori, what works in sporting context, whatever video evidence exists, and reports from first-person usage of the techniques and principles. There are probably sources I'm leaving out.
Now, is it helpful if the person teaching has direct experience using the techniques a lot in a defensive context? I suppose. The problem is that I literally know of nobody who has that level of experience in any given art (there surely are some, but I don't know them), outside LEO and folks like bouncers (who have a different objective/purpose/focus than straight self-defense).