I think there have been plenty of studies done, both statistically and psychologically, regarding the value of training. Please refer to "On Combat" and "On Killing" by Lt. Grossman. Refer to my previous stats, which were dismissed, regarding hunting. Please refer to "The Talent Code" by Coyle regarding practice. The fact is that training and practice improves skills. The government, in some states, uses this factual concept to give a compelling reason for required training.
And no, I don't think the average gun owner or carrier will actively seek training on their own and I don't think they will practice properly on a consistent basis. And no, I don't trust that all "lifelong shooters" received good training or quality advice from their parents, grandparents, brothers, etc. Some did, I'm sure, but I'm also sure some received extremely poor advice and spent their weekends shooting propane tanks with pappy.