As seen through the research from Stan, Peter, Ellis, and a myriad of others, Ueshiba was more than capable of handling himself against challengers. Even during his time with Deguchi, Ueshiba was learning aiki, learning Internal Power (IP).
Read this very informative post regarding IP:
I dont doubt that, and have read it all. What is new to my is that you seem to argue for a spiritual/ metaphysical relevance of aiki, which is not what I myself find in the authors you quote. I even seem to remember Mr. Amdur arguing IS has nothing to do per se with personal development, character.
Aiki is formless and the basis of a very strong, powerful martial skill that is imbued within one's body, mind, and spirit. It transforms from a "skill" into One's Self. As Ueshiba replied, I am aiki.
Think about building a powerful, strong (not physical) budo body that instantly and appropriately changes incoming force and energy such that it is dissipated or returned or used in some manner to nullify the attack. Imagine Tomiki as he stood there and watched as judoka tried to throw him and failed. Takeda tossing Ueshiba around like a rag doll, even though Ueshiba was famed for his physical strength. Imagine the freedom of movement, freedom of martial ability that this conveys. And then imagine the freedom of spirit that is a byproduct of this. Now imagine Ueshiba putting all of that formless aiki, formless freedom of mind and body and spirit into his spiritual vision.
Ueshiba knew the formlessness of aiki. Knew that it could be poured into one's spiritual nature and have it fill that vessel. IMO, it's why he said no one had to follow his exact footsteps.
Again, I am agnostic as for the historical examples, I have not been there.
With all due respect, I think you are charging "aiki" with a metaphysics that is entirely your own. Invincibilty can lead to freedom? I doubt it. It can lead to megalomaniac fantasies that are not very spiritual at all (and which, ironically, O-Sensei probably also had...), and will likely cause harm if one does not engage with them very very carefully.
But thanks for the discussion!