Has anyone done tests on cadavers, or large animal carcasses?
Yes.
How about studies from police coroners, maybe?
Yes.
Just like with the arrow examples you noted above, not all arrows worked all the time depending on the angles hit, bones hit, tissues, hit, etc. Same for bullets.
The one thing arrow makers testing carcasses have found out just like the bullet folks is that shooting dead things always produces a stop and shooting live things does not.
Funny article. The guy wants "stopping power" dropped from use but then continues to use the phrase in the article and even offering what should be the correct definition of it, LOL, and that definition being rather vague, covering two of the suggested possibilities listed.
Strange that as a doctor, he has failed to note that ammunition, like medicines or medical treatments, doesn't also work of a given individual in a given manner. He can't tell me that my broken leg will heal in XX.xx days or exactly how well my leg will feel in XX.xx days, despite being a surgeon. He can't tell me how much pain reliever is needed to relieve my pain sufficiently despite countless studies in that area of medicine.
If human bodies were 100% uniform with one another and people getting shot were getting shot in 100% uniform manners with 100% uniform ammunition, etc., then we could expect 100% uniform results, but still would not get them. However, human bodies are not 100% uniform. People's attitudes and behaviors under stress and in responding to stress are not uniform. When people get shot, they don't get shot in a uniform manner to everyone else either.
The problem isn't so much with using ballistic gelatin as it is with the combinations and permutations of variables that influence whether a given person being shot will be stopped or will not be stopped. These certainly include but are not limited to ballistics, bullet construction, velocity at impact (relates to shooting distances), angle of entry, trajectory through the body, health of the individual, size and shape of the individual, mindset of the individual, etc.
As we have seen all too many times, the difference between life and death can come down to mere fractions of an inch and so mere fractions of an inch difference can be what influences differences in performance. When Doc Vail can control for all these combinations and permutations, then maybe we should consider revisiting whether or not gel testing is valid or not.
{I see Frank's and my posts overlapped. His answer is probably much better}