I've just never known anyone in aikido to describe aiki as a literal power that goes from nage into uke. I've always heard it described as more like a "condition" that results from moving harmoniously with the other guy.
As Sagawa describes it (and as was said of Horikawa), aiki is a power that you inject into the other person's nervous system even without any physical motion at all.
I find that pretty unique, though as you say, it seems consistent with CMA use of jin.
David, I agree with your posts. I think the idea of "aiki" as a singular type of power is simply a misunderstanding of the idea that there is a power that when used properly in regard to an incoming force causes "aiki". It's a misunderstanding and I tried (half-heartedly) to archive the idea that some people are misusing the term "aiki" as a power itself, by not being clear.
In the same sense "kokyu-power" is being misused also. The power of "kokyu" is the same power that is used to create "aiki". "Kokyu" denotes the breath-related training that is used to develop the "jin" as it increases in power. As Ignatius mentioned, there is only one jin. The old saying is that "there are many jins but there is only one jin". That jin skill is the basis of "aiki", of "kokyu-nage's", of "fajin", of Tohei's "ki-tests", and so on. There is no separate power that is "aiki-age" and "aiki-sage"... those are just examples of the force-skills known as "jin". "Aiki" is a particular way of blending the jin with an opponent's attack so that the opponent's own power is used to throw/technique him. There should be, as you noted, no resistance.