kids today can reach age 18 without ever having been struck or striking anyone else. Combatives are mostly a way to let people hit others and get hit and learn that the world doesn't come to an end.

Various forms of combatives are used by various units and forces but few are really combat skills. The reason for that is the true infantry hand to hand combat skills are -- or certainly should be -- deadly. Literally. Few forces today are willing to impart such knowledge to average troops due to fear of misuse.

Schmedlap is totally correct:
"...When you practice the wrong technique - which is more likely to occur when you first practice it while exhausted - then you develop motor memory of the wrong technique. Learn the technique, get it right (in other words, train). Then, when you're proficient, you can do it while exhausted for your day of conditioning.
That's important...

However, I think on this:
We don't do stress shoots before basic rifle marksmanship."
We need to do the same thing -- get the basics thoroughly embedded using enhancements to this methodology (LINK) then go to stress shoots. Combat is a stress shoot..