If for no other reason, that Takeda Sokaku, followed by all of his successors, reversed the general koryu bugei arrangement of uke and tori, establishes that they were doing something different. What was that difference?
Oh, by the way, before I go any further, teachers rarely teach ukemi. That's the job of sempai. It's clear from the pre-war Ueshiba film that someone taught the students ukemi, as they are following classic form, and, unlike judo, Ueshiba is not throwing in such a way that, if you relax, you'll end up in that configuration. It takes some skill.
1. No way would Takeda allow anyone to put him in a vulnerable position! He wouldn't even take food, untasted, from students, stabbed his own child when the little boy puts a blanket on him while he was asleep - it would just not happen.
2. Aside from that, the principle that the early teachers were presenting - DR/aikibudo - was of people of superhuman strength and ability. (See upcoming TIE of Goldsbury, where Ueshiba asserts to Hashimoto Kingoro that one of his trained students was the equal of any ten ordinary people).
3. So the early model was that, through aiki - whatever you want to regard it - the skilled person was undefeatable. One learned by feeling what the teacher did to you and tried to replicate it (or, if lucky, got actual instruction in some explicit training methodology). (Part of that process, according to Sagawa Yukiyoshi (quoted in HIPS
and paraphrased here) is that aiki is developed by taking a lot of hard ukemi).
4. An interesting quote
from Andrew Smallcoombe - "It confirms some of the things Kobayashi Sensei used to talk about after early morning training - being the first to actually teach ukemi to beginners . . .
5. More Importantly
Nakayama: I was treated in the same way as the more experienced practitioners, since I was Kobayashi-san's younger sister. You could say that I learned ukemi naturally in order to avoid injury, or you could say that I was made to learn...
Kobayashi: Ukemi and those things were not taught, we would do suwari-waza, so you would naturally roll around from a low height. However, those you couldn't endure it would end up quitting.
Kobayashi: His body was highly conditioned. Everybody flew when they were taking ukemi, but that was because if you didn't fall you would have been slammed down. That gradually changed to jumping, and just showing the form of falling... It wasn't like being thrown by a normal person, it felt as you were sinking into the tatami. From that sharpness things mellowed over the years and come to be expressed in Kata. We who were there take ukemi based upon our experiences from that time, but those who have only seen the later form don't really understand. That in and of itself is a reason for the change.
(By the way, note that Ueshiba still "had" it through the 1950's, perhaps the early 1960's, because that's when Kobayashi was an uchi-deshi).
And from the THIRD
Moderator: In the practices before he passed away, did it still feel as if you were sinking into the tatami when your were thrown?
Kobayashi: At that time he had entered into the realm of Kata, we had experienced the changes up to that time, so it was okay, but it was a problem for people who only imitate that period.
And from the FIRST
Kobayashi: It was exactly the same, the same, but joint techniques, techniques that twisted and strengthened the joints, were the most common. To my recollection, techniques like Kokyu-nage were only done after we started giving demonstrations. ](note: this probably relates to Ueshiba's concept of using joint techniques to soften the body, which he called kasu-dori - without the "softness," the higher level techniques were, if I'm correct in my inference, regarded as impossible to learn
Since it would be just unbearable to watch everyone do Ikkyo or Nikyo (in a demonstration) they created techniques that could be done with a single movement. So, if you did those techniques in front of Ueshiba O-Sensei you would be scolded. He'd say things like - it's just impossible to throw anybody that way.
Moderator: Did O-Sensei use those kinds of techniques?
Kobayashi: He would do techniques that were similar to Irimi-nage, but we were just imitating those things for the demonstrations. So if we did those things during training we would be scolded.
There's a smoking gun. The problem is not ukemi. The problem is that many believe that uke "takes falls" to create the form - the kata, as opposed to really, genuinely, unavoidably throwing the individual.
Hopefully saving how that is done for another venue, there is no doubt that Kobayashi, on the cusp of the transition of Osensei's technique (which, it appears, happened in the late 50's or early 60's, NOT pre-war - note that Shirata Rinjiro stated that Ueshiba as at his peak during his Iwama years) - - - -observes a change in how ukemi was done - and techniques executed.