Kote Gaeshi, the wrist return is a classical aiki throwing form. The physics of it seems irrational to the new student. How could a person be thrown from a wrist connection into a head over heels flip?
The answer that is given by many Aiki teachers is
In my humble opinion training with this view on the mechanics is a huge heap of manure. What they are really saying is, "I have not figured out the mechanics of the throw yet, so I conditioned this guy to jump over for me."
To be a real and effective technique kotegaeshi must affect uke's center, distort their structure and break balance. Any pain on the wrist comes from stylistic temperament and ethics, improper use of power, or flawed application of mechanics.
Application of the lock should transmit energy through uke's elbow, shoulder, and torso. Kote gaeshi is not a wrist break, it is a connection from one center of balance to another's. Pure and simply it is connection. The best artists can do this technique without any pain, and virtually no detectable pressure for the proprioceptive nervous system of uke to register. This, in my opinion should be the highest goal of all artists: no pain, minimal pressure.
So why do people flip out of the technique?
Simple answer is because they were told to. For the vast majority of kote gaeshi throws actually an easy back fall would suffice. In the past five years I have only been forced to choose a flipping break fall maybe twice. Sure I bet someone out there can really nail it, but for the several hundred thousand of other practitioners, we are playing make believe when we take these throws. Yes there is collusion in the way aikido is often practiced. It is ok, as long as you recognize it, admit it and are using it as a tool to get to the next level.
A few years ago I was at a dojo and a man was fervently arguing that a flip was the only proper and safe way to get out of kote gaeshi. He was upset that I could always take a easy back fall out of the technique. "Really? Ok I will tell you what, I will throw you ten times as hard as I can and you have to take the flip, and you can throw me ten times as hard as you can, and I will back fall. That way we can see which method of ukemi is superior" He agreed. I bowed off the mat, put on some slippers and walked outside into the parking lot. "Where are you going?" the man asked. I responded "We are doing it out here on the concrete." I casually kicked some broken glass, and sharp rocks out of the way as he declined the invitation to demonstrate the superiority of his technique in non ideal conditions.
Sure I know, your Sensei could throw me and make me flip. I know, I know. There are many circumstances were this condition happens, but the flipping ukemi is one possible falling reaction, not the rule.
So why do most aikidoka flip out of kote gaeshi? I believe it is the collusion that flaws much of our practice. There are artists that can make it happen, yes. So we, the humble students, try to copy the example without understanding the mechanics. We have to justify the flipping action great sensei got that alludes us so we rationalize an excuse. We tell people they better flip or their wrists will break, and we perpetuate a false myth about the practice. We then practice aikido that looks like the way the high level teachers do it, but it is a pale imitation. The collusion kote gaeshi techniques are a mere phantasm of aiki. They are a faux reflection lacking the substance and mechanics of a martially valid expression of principle.
You can probably write a book about what happens to a person going through a masterful kote gaeshi. "Flipping out to avoid the wrist breaking" would not be in it.