I did a body mechanics class a couple of years ago at the Okinawan Karate Union summer seminar, and my uke was a volunteer black belt that had never seen or trained with me before. I was especially careful not to hit any "critical" places, or to cause him too much agony with kyusho strikes.
It was a great class, and when it was over, the same kind of discussions were held... "would this work?"... "do you hit like this...?" etc... with a million different questions being asked. What put a stop to it was the uke himself telling everyone... "I don't know what those strikes looked like from your perspective, but he lit my a$$ up every time he touched me..."
I was being exceedingly gentle with him, and he told me later that it still almost put him out a couple of times. Hitting the nerves and points in the right order, and at the right "weight" of strike, and proper angle, is what makes kyusho so deadly because the body is predictable... and strikes to certain nerves cause specific reactions, whether it's to raise the blood pressure, increase the heart rate, or cause a blackout. It isn't something you learn in a seminar... or in a "few classes". It takes concentrated study, and an understanding of exactly what's going on... which can take years to absorb.
Kyusho jitsu isn't just "points", but "methods of hitting the body"... so, as Oyata Sensei was showing, the 5-finger strike may be more applicable in one area of striking than the fist... and the "crane's head" may be better suited in another spot. It all depends on application, body structure, nerve locations, and how the attack is structured, so you know where to go for defense. It takes a lot of "scenario training" and rote practice (much of it without touching each other) to get the movements correct.
If you noticed, Oyata Sensei was using some very fluid karate blocks and strikes in his kyusho hits, so his method looks much like slapping, but there are some "hidden skills" inside of that, so it isn't just simply "hitting the points", but a lot of method, sequence, correct angle, etc. that add up to some very effective, yet "light" strikes.
Kyusho can be deadly, and have long term effects on the ukes if they don't get proper care. Points in the wrist affect the lungs, and a lot of jujutsu and Aikido practitioners develop asthma and respiratory problems if they take too much abuse there without getting the proper "balancing techniques" applied to counter the damage.
While there aren't really a lot of "secrets" left in the martial arts, there is a lot of information that is still below the surface. When we talk about "living the martial way", it's because to learn that information requires more than just showing up to train twice a week. It takes study both inside and outside the dojo, and training that, like Oyata Sensei's, seems a bit rough on the uke.
There's no "easy way" to teach shime waza (chokes) without putting someone in a hazardous position of being choked out, and needing resucitation, so learning the skills involves "getting involved". It also involves the amount of knowledge your teacher has, and how well they can pass it on to their students.
If you remember what Miyagi said in the "Karate Kid"... "everything not as it seems"...
It was very true...