Rather than DGU or other clinical terminology, can we agree call it shooting people? Defensive Gun Use is another euphamism, as firing at someone is not defensive- it's a counterattack (please note I am resisting the urge to hyperbolicly ask if you expect your bullet to defensively deflect the attacker's shot) No issue with that per se, I am an advocate of violence as a problem solving measure and am comfortable calling a spade a spade.
No, I'm quite comfortable sticking with DGU since it is more accurate than your suggestion. "Shooting people" is a subset of successful DGUs. "Defensive shooting" and "counterattack" are not mutually exclusive terms, however, the latter encompasses both non-lethal and lethal use of force. The former is a commonly used term in the literature when referring to DGUs during which the weapon is fired, so I will continue to use it.
Regarding philosophies of self-defense, I have not studied it but am I correct in reasoning these broad generalities?
1. Establish order of expendability, both in general beforehand and situationally.
2. Take whatever neutralizing action, starting with the least destructive, that is at your disposal to preserve your life and well-being while inflicting as little damage as possible to others, in order of their expendablity.
No, "expendability" is not a consideration and things often happen far to fast for such a thought intensive process. The nutshell version is more like, (1) identify and access the threat and (2) respond with the appropriate level of force. If it's a non-lethal threat, respond with The degree of non-lethal force necessary to stop the attack. If it's a threat that puts you in reasonable fear of grave bodily injury or death, respond with lethal force. In either case, if retreat offers the better chance of going home, go home.
Now before I hear the "judge, jury, and executioner" comment again, responding with lethal force does not mean the goal is to "shoot to kill". The goal is to stop the attack. Now. Definitively. While it's true that putting rounds on the center of observable mass has a high chance of being lethal, death is not strictly required so long as the attack is stopped. In other words, if the assailant reconsiders his life choices after taking one round to the chest that doesn't kill him...well...as I wrote earlier: success. If I choose to keep shooting after that, I am no longer defending myself.