Can't speak to human targets. However, as a bird hunter having shot many hundreds of birds on shooting operations and in the wild. I can vouch for the real world FACT that multiple pellets striking a bird AT THE SAME TIME tremendously increases lethality. That's why the 16 ga. and the 28 ga. are so lethal in comparison to other gauge shotguns.
As they have the shortest "shot strings" and the pellets strike at essentially the same instant. Other gauges take a few micro seconds to put the same number of shot on target.
Somewhere around my house I have a scientific paper which "proves" that it takes at least 1/4 oz. more shot in a 12 ga. to equal a 16. ga. with the same shot. Of course liars can prove any thing. But my experience has made me a believer that there is validity to "short shot strings" kill better, faster, on birds.
A 16 gauge kills more birds "dead right there" as does the 28 ga. Little wounding, no flopping, just "bang" and the dog retrieves.