Apparently the Marshall/Sanow study from the 1980s only looked at handguns and the most popular caliber of police rifles. Not shotguns.
This other person did his own study that included rifles and shotguns, but he lumped all centerfire rifle calibers together, regardless of bullet type, and ditto for shotguns. All gauges were added into the database, all loads from #9 birdshot to 1-oz. slugs and everything in between.
This study showed that shotguns were a little better than rifles, and rifles were a little better than .32 caliber pistols, and all other centerfire handgun calibers were not quite as good as .32 calibers!
https://www.buckeyefirearms.org/alternate-look-handgun-stopping-power
Maybe we should consider that .32 performace a fluke as there were only 25 shootings involving that caliber that were part of this study. Only the .32 and the .44 Magnum had such a small number of incidents; all other calibers had approx. 100 to 400 shootings in the database.
BOTTOM LINE:
I think of 12 and 20 gauge shotguns with buckshot, or slugs, as being equally good manstoppers as .223 or 7.62 x39 carbines at typical home defense distances.
If there's any difference in their lethality, it's not much. Not enough to worry about.
Recoil, ammo capacity in the firearm, range, and the speed of reloading are all more important, and ALL of those factors favor the rifle calibers.
That being said, I've owned a number of combat shotguns that only held 5, 6, or 8 rounds. One of them I will still occasionally prop in the corner of my bedroom for home defense and to deal with things that go bump in the night.
I don't feel I 'need' a 30-round magazine.
But, intellecutally and rationally, I think a CAR-15 with a 20 or 30 round mag and a good flash suppressor (or silencer) beats a shotgun as a defensive long gun.