Richard keep in mind you are referencing your military experience but the civilian experience and equipment is much different. The old 1911 .45 you carried in Viet Nam was likely an old WWII era pistol, and while those pistols were pretty functional, they sure lacked a lot in the accuracy department due to their extremely sloppy fit. A good Les Bair and many other custom .45's can print a 1 inch group at 50 yards. Even many of the newer off the rack guns can do 2 inches at 25 yards. So the design CAN be accurate, it just depends on how they are made. As for your Barretta, yes it was a more accurate gun out of the box in its military trim, and can be hand fitted for even more accuracy.
Now on to the modern ammo. Of course the military is ordinarily limited to FMJ ammo so if that is the way it has to be, I would rather have a 230 grain .451 bullet to fling at my enemies than a 115 grain .355 bullet. Hence the .45's reputation as a better manstopper by far.
But us civilians can have ammo not approved under the Geneva convention. And defensive ammo has all gotten better even in the last 10 years and is under constant development. While some might not agree, the 9MM with the proper ammo is an effective manstopper. In fact the FBI is now transitioning their agents back to the 9MM from the .40 S&W. This represents a full circle from the 9mm back in the 80's to the 10MM after the disastrous 1986 Miami shootout to the .40S&W when the 10MM proved too much for most agents to handle (the whole reason for the creation of the .40&W) and now back to the 9MM. Yes the new ammunition is that good.
The 9MM is now an effective manstopper with the right ammunition, offers much less recoil, meaning that follow up shots are much quicker, and carries more ammo in a given magazine size.
The 9mm is an effective man stopper, but one reason many dept. went to 40's , is because the 9mm has a tendency to go through someone and hit someone else, The 40 does'nt. The 9mm will penatrate car doors, the 40 has a harder time.