gel.....and denim. The purpose of 357 sig, to penetrate and stop the target. Windshield, sheet metal, light body armor, etc.....that is what 357 sig will do for you, and still stop the target.....sorry, but 9mm won't do that the same way.
also, I won't trust anything from "ar15.com"......I wonder why they didn't compare the damage of the 30 carbine vs 5.56
Human tissue analog and clothes. You having to shoot through windshields or body armor is 1000 less likely than another person and that is unlikely.
If you actually read the report, you'll see where they got their data.
The 9mm worked just as well as the .357 Sig. I'm sorry that doesn't fit with your preconceived notions, but them's the facts...