Let me start by saying I yield the point.
Anyone who has had quality training (formal or informal) is going to have an edge over someone who just bought a gun one day. Of course, as you said, everything is subject to time and luck.
" firepower, terrain, time, strengths, weaknesses, and leverage "
What sort of self defense situations do you think the average joe civilian is likely to find himself in? Unless we are talking about swat (and they are overdramatizing the scenario the majority of the time), military, or a zombie apocalypse in the real world you've got someone trying to murder you (or family), rape, mugging where the crook isn't willing to settle for just the cash, kidnapping, and home invasion. As far as guns are concerned Joe needs to know how to hold the weapon correctly in a tight grip with a solid stance, aim for center mass, and to only shoot if he or someone else is going to die otherwise.
If Joe civilian has the time to sit and formally categorize and assess the tactical position he's got to be the bad guy, in some less likely than a lightning strike situation (terrorists, mass shooting), or he's lost it and is going vigilante. It's not a movie, Joe shouldn't be running around taking out the armed gang that's robbing the bank.