This type of scenario should probably not be something that a gun-toter hasn't considered or come to terms with. That said, personal grit, nerve, detecting the danger within a reasonable time and coming to terms with exactly what a person is willing to do in order to protect themselves is probably going to be more critical than absolute shooting skill. Sure, a person need not be bumbling ( thats for sure) and a person should train and maintain a reasonable level of shooting proficiency. I agree that people are not trying to be slower or less accurate but shooting skill and "fighting with a gun" are often different things. I am simply a proponent of keeping all those issues within proper perspective. Knowing how to size up a situation, having a good idea of what to do first, understanding how best to exploit conditions in your favor and making the first couple of decisions at the onset of a conflict, ( good ones) can certainly be a game changer.
Plenty of people are a good enough shot to get things done but in many instances, many of those same type of people are conflicted about what to do and what they are actually willing to do in an armed confrontation. Moral dilemma, ethical dilemma, legal dilemma, confidence dilemma, psychological dilemma, emotional dilemma, skills dilemma. I think that all those things may need to be sorted out and put away before a person can effectively address or face down evil doers. Perhaps some people square those things away innately or perhaps easily, quickly naturally but I am sure that many do not. Sometimes it takes a little honest and purposeful introspection. Shooting skill might actually be the easy part when considering all the boxes that likely need checking in order to be a competent defender.