Well, son-of-a-gun, Nuke, ya got me thinking some about my past ! Now, my past was a long, long time ago, but some of the ancient concepts may still apply. Let's see:
A good guy shoots at a bad guy. Consider "fire" probability (a discharge occurs), then, "hit probability" (the bad guy takes the projectile), then "kill probability (the bad guy is ineffective), then lethality (the bad guy, or assembly of bad guys, is/are dead). The bad guy can be one individual, a bunker, a tank, a plane, etc. With respect to handguns, I think the military, the LEO's and the civilians have different concepts and ideals with respect to the defeat of the bad guys. Let's assume that the military shooters are in groups: They are all trained, but the good ones survive to do it again and again. They learn to use what they are provided or what they can get on their own. The LEO's are also trained but rarely engage in a life threatening situation. They may swager a bit, but most of their time is spent in non-threatening situations. So---what do they need--- something easily controlled and relatively reliable (hit probability). Since there appears to be no "thing" as stopping power in a handgun, multiple hits appear to be a worthy goal. Us civilians, however, appear to be able to afford good weaponary, lotsa training (our own $$$), lotsa interest and desire, and sincere motivation to "do good" with respect to our loved ones and neighbors. We are rarely at risk but practice frequently.
I was trained that "2 in the body and 1 in the head" was perfection. I am now old-----my objective is for as many hits to the body as I can manage. It is easier to miss the head than the body. Does it make any difference which bullet (9mm, 357SIG, 40S&W, 45) hits the body ? Sure----but out of 4 shots, how many hits can you (me) deliver. I'll take the 9mm and hope for lotsa hits.
About the long gun change in objective: If I remember correctly, the .223 "tumbles" a bit during it's path toward the target. WOW ! A high velocity tumbling mass vs. a moderate velocity linear mass. Think about it. I do not want to be behind a brick wall if being shot at with a barrage of .223 ammo.
I do not think there is a definate answer to your question/quandry, but I think there are definate answers to situations that are significant to survival in the most confronted situations of the group (military, LEO, civilians) trying to survive.
I am now a non-combatant. I want to protect my loved ones and myself. I will use that which is comfortable and "lethal" for the encounters I somehow expect. The second sentence of the second paragraph is my mantra.
Keep thinking, Nuke, you are on the right track. You are the future.