Several good points here.
One, people aren't made of ballistics gelatin.
Two, it's going to be darn near impossible to hit Center-of-mass without involving some form of bone or cartilage. Either will reduce penetration.
Three, while we are NOT FBI agents, it's good knowledge to know just how our self-defense rounds work in the case of a miss. How dangerous are they if they fly past the miscreant, and impact a car, or glass, or even a door or wall. Hoping that they will stop the round isn't exactly the kind of thinking that one makes plans on.
Gunfights are dynamic events. Distances vary, barriers change, and the rapid actions of both parties can make a mockery of all of the "testing" in the world. Let's face it, JHP rounds in a .380 ACP aren't known for deep penetration with wide expansion. Most JHP rounds also have reduced expansion and penetration when barriers are found in the way. Energy can do both features, penetration and expansion. However, both will re reduced as the available energy is used. Looking at the FBI protocols, note that the rounds meeting them are all +P. There's a LOT of work involved in barrier penetration and expansion. The round meeting all of the protocols also tend to be of Duty Length, to get every erg of energy available into the performance of the round.
In the end, the shooter picks what he or she believes will work best for them, in their own particular circumstances. Of course, nobody should overlook other considerations. The round must be accurate, reliable, and controllable in the firearm it's used in, as well.
These rounds are tools, and may well add yet another facet in the choosing for some.