Re: Defining the word "Aiki" and looking at the phenomenon it describes.
I have a different view. It is not something IMHO which gives one great physical ability. It is an ability where you would put your partner to feel the effects of the laws of nature to its maximum.
Uke does not have one opponent but two: Nage and the laws of nature (eg gravity, leverage, centrifugal force, etc). My theory is that uke does not submit to nage per se but to the effects of the forces he uses. Everybody succumbs to the laws of nature. No one is immune. This is my interpretation of Osensei's saying that you are the universe.
That is why it is possible in the example of Endo sensei's case where he does not grab uke or in the case of Saito or Hikitsuchi sensei to do no-touch aiki techniques. You can also validate these theories in the dojo if you know what you need to use.
At it's highest level imho, you can actually "remove" nage during the technique and uke falls by himself since nage does not rely on himself per se for the technique but on the effects of the forces. It is the forces that are strong and immovable and it just reflects on nage. That is also why a lot of people view aikido's techniques as magical yet they are not.
As always, this is just my own interpretation.