I am pretty confident I can rack the slide quick enough in most cases, but I agree, there could be situations where there isn't going to be much time and in those instances I probably won't be relying on the gun; god forbid it ever comes to any of those situations. That's what practice is for, and for the carry gun, there should be plenty of practice.
In the example of the 71yr old guy, he had enough time to draw, rack and aim. Can't really see if he did, but there was enough time to do it before they were even aware he was doing anything.