Your post poses a logical question, but I am inclined to question the underlying "facts." I was quite surprised to see you quoting 16 - 20" of ballistic gelatin for JHPs. I wasn't aware that one could always count on that from FMJs!

BTW, there is a notable body of thought that even the danger of overpenetration itself is exaggerated, particularly considering the drastically decreased velocity of a projectile which has passed through a body. Some who share this outlook consider misses to be much more dangerous than shoot-throughs, particularly because there seem to be so many more of them.

AFAIK, a significant number of commonly carried defensive loads UNDER-penetrate. Of the ones that overpenetrate, few are JHPs. I am certainly open to your quoting results which indicate otherwise.