The point of the testing is to see how the bullet will perform, whether it will expand at a given velocity, and how well it will penetrate, in a repeatable tissue simulant.
But, none of that correlates directly to whether it will, or will not, result in a disabling hit on a human target.
This is the point. ALL testing in any medium only proves what the bullet will do in that medium. It does provide a consistent material, and therefore useful to make relative comparisions between bullet performances in that medium.
We ASSUME similar performance in similar media, but even the best simulations are just that, simulations, and cannot take into account or replicate the massive amount of factors involved in real world shootings.
Just as relying on the math alone can present a distorted view, so does relying on gel tests, as the sole determining factor in what is most likely to be most effective.
The idea that round A will be more effective because it went 3 inches deeper in the gel than round B is not only a blind alley to go down, but an extremely narrow one.
Point here is that even if testing accurately mirrors real world results 80 or 90%+ of the time, there will still be real world factors that testing couldn't account for that can change the outcome, radically.
A big example of those "rare" exceptions is the FBI's Miami shoot out. The 9mm JHP that "failed" to stop the bad guy "fast enough" was a fatal wound. I've seen a surgeon's comments on it, and he stated that if the guy had taken that wound at the operating room door, it was unlikely they could have saved his life. Absolutely a fatal wound. Just not a immediate stop.
The round used met every testing standard of the time. Including penetration. It just turned out that in the real world situation where it was used, with all its complexities of angles and materials, meeting the approved requirements just wasn't quite enough.
Since that event, requirements have been changed, and better bullets have been created, and tested.
Don't take meeting (or even exceeding) official standards as a guarantor of success. Its not. There will always be situations where factors combine in just the right way to create a situation where official performance standards just aren't quite enough. Doesn't happen the majority of the time, but it absolutely does happen.
Even the most highly rated rounds have examples where they have failed, and oddly enough, there are also examples where the most denigrated rounds have succeeded. There is no magic bullet, and nothing can be guaranteed to work 100% of the time, or, at least won't be, by anyone honest.