With all due respect, it seems that you misunderstand the nature of the counter-arguments you claim to have addressed.
One could fairly credit you with having made an interesting circumstantial case on the basis of carefully selected quotes organized on the basis of a number of inferences you have made from your personal training experiences.That is something very different from your apparent belief that you have made a rock-solid case based on hard evidence. You find your argument compelling. Fine. That still doesn't make it rock-solid.
What I mean by "hard evidence" is a confirmation of your case by an individual who was familiar with Ueshiba's practices -- as both a private individual and as a semi-private or public teacher/exemplar of his art, and/or by textual evidence with a clear provenance.
One can entirely accept the argument that any number of people who were students of students of Morihei Ueshiba, Kisshomaru Ueshiba, or Horikawa Kodo, or (fill in the blank) find something valuable in the mode of practice you favor without accepting the assertion that either the mode (or precise goal) of your practice is identical to that of Morihei Ueshiba.
In a koryu context, if a school had "lost" such material from its core curriculum (let's call that the "honden") and subsequently "re-imported" the material from some other school that had somehow gotten hold of and maintained that body of instruction, unless there was clear documentation (which requires either unequivocal textual evidence or confirmation by someone familiar with the original material as-taught, or both) that each and every piece of the re-imported material was identical in sequence and detail the original, the material would have to be reclassified as "outside transmission" or "revived transmission." And the final decision would rest with an individual who was appropriately trained and licensed to do so. It would would never be treated as part of the core teachings faithfully transmitted through an unbroken sequence of exponents.
It's not a matter of whether the material is good stuff, is related in some significant part to some good stuff that was part of the school three-quarters of a century or a century ago, or if the people working the material are good people.
It's a matter of whether there is sufficient documentary evidence and direct first hand knowledge to state, unequivocally with no missing links in the chain of argument requiring supposition or inference, that "this" is exactly "that," whatever this and that may be.
Yes, you can say (not unreasonably) that there's no way anyone can know whether or not "this" is good stuff, or useful stuff, without experiencing it. That makes perfect sense. But that is a fundamentally different assertion than the claim that "this IP/IS practice,the aiki body it develops, and whatever arises from that is nothing more or less than Ueshiba's aiki."
Frankly, the only way I see to closer to proving or disproving that claim is for some intrepid researchers currently in Japan to follow up some of the research suggestions Ellis has repeatedly made. There are individuals still alive and related schools extant which might be able to provide further evidence to confirm your informed speculations.
But absent such evidence, your assertions remain informed speculations. While there is value in informed speculation, there is a valid distinction between informed speculation and proven fact. My sense is that the frustration of your interlocutors turns directly on what they see as your (relentless) refusal to acknowledge that this is a meaningful distinction.
None of this goes to the additional questions of whether or not Ueshiba's training methods, philosophical views, religious views and practices, political or soteriological goals changed over time, or to the question of whether what attracts people to the art is simply the fundamental physical ability to manifest rootedness, and generate uncommon power by which the movement of others might be directed, or some other, perhaps less tangible feature. My experience is that most aikido practitioners have some measure of both, but the proportion varies widely from individual to individual and the spectrum is a broad one. Very few are interesting in a strictly physical approach, even a highly nuanced physical approach like those found in the various IP/IS models available.
To return this to the OP. "Awase" can be accomplished any number of ways. Would "aiki" as a distinct principle be useful in accomplishing "awase?" Sure. Is it necessary? Not remotely. Is it desirable? De gustibus non est disputadam!
If you don't like what's on the menu, there's no need to go in the restaurant and no need to fuss at the people who do like what's on the menu. It may be quite enough to say (as F. Scott Fitzgerald once paraphrased Lincoln) : "If you like this sort of thing, this, possibly, is the sort of thing you'll like."
That formulation is well within the Confucian edict "To go too far is as bad as to fall short."
Mindful that this guidance is well within the broad sweep of traditional East Asian shared culture with which Ueshiba M. was raised and to which he was devoted, yet fearful that it is already far too late in this reply to even say such a thing, I will close in the hope that all of the above sparks more light than heat.
With respect, I do understand the nature of the counter arguments. Let me sum it up:
People who have provided no research, no evidence, no far ranging experiences telling me I am wrong in regards to Ueshiba's aiki. Now, these people point to a student of a student of Ueshiba for proof. I point to a student of a student of Ueshiba. Who trumps whom? Beyond the fact that each of us is merely pointing at external sources, in essence, these people absolutely must know
what aiki is to emphatically state that I do not know what it is.
As you state, "It's a matter of whether there is sufficient documentary evidence and direct first hand knowledge to state, unequivocally with no missing links in the chain of argument requiring supposition or inference, that "this" is exactly "that," whatever this and that may be."
Let's apply that logic to the "counter arguments" shall we? Except, no one has, no one will, no one cares to. Rather, it is taken unequivocally that those with "counter arguments" know absolutely the knowledge to grant all that I do not know.
Let's go back to Ueshiba. Can these people replicate his skills? No. Can they replicate his knowledge of ancient martial concepts? No. Can they prove his training? No. Can they prove his practices? No. Which sort of puts us all on equal footing, no? What, then, gives them the foundation to state so emphatically that I am wrong? If we apply your logic to their arguments, they fall far short.
So, let's go back to the research and the experiences. I have done the research. They haven't. I have about 20 years of aikido training. I'm sure they do, too. I've trained with a variety of aikido shihan. I'm sure they have, too. I've trained with the IP/aiki exponents. They haven't.
Who, then, is on solid ground? And who is on marshy ground?
And this is all just going over what I have done. Shall we toss in Marc Abrams, Chris Li, Greg Steckel, Rob Liberti, etc? All who have greater experiences with students of students of the founder?
Shall we toss in the interviews with the students of the founder themselves who stated they didn't know what he was doing or how he did it? With Kono who said everyone was doing everything different? With Pranin stating that Ueshiba was rarely at Tokyo hombu, let alone teaching there. Etc, etc, etc.
As to the koryu example, let's apply it to aikido. We have several branches from Sokaku Takeda, passing on aiki. There were peers with similar training methods. There are exact training exercises between aikido and daito ryu in regards to training aiki. Where is the broken transmission? Maybe it is that people just didn't know it was there and that these people are arguing from a basis of ignorance rather than supported research? Except that no one wants to apply the same logic to their "counter arguments".
So, it's fine for someone to state unequivocally that awase is the principle of aiki and is what makes aikido unique, in an unsupported manner, but not okay when I refute it backed by research, Ueshiba's own words, and direct experience? Really? Can we use your logic to ask them to support their words with "rock-solid" evidence that I'm asking to provide? Show me Ueshiba's own words that supports their case. Show me the experience they have with those who can do what Ueshiba did that supports their case.
Again, I stand by my first sentence in that post. It has proven true time and time again.
When all logic, research, evidence, and truth fails, talk about character or belabor the format.