Maybe this will help explain my conceptual point. I wasn't trying to say that "aikido" was being demonstrated in MMA, I don't think it is. I do however think that "aiki" is there, and that "aiki" is all over the place in almost any/all high-level martial arts, even if it is not recognized as being so in that art.
Perhaps this is a good way to try to explain what I'm driving at. O-Sensei didn't "invent" aiki in aikido, he "found" it... if that makes sense. It was there, waiting, and he found it, thought it right and good, and built a system of principled reactions to aggressive physical actions which seemed to transcend the merely physical and go into less physical realms.
I am not one for the non-quantifiable, I apologize. However, I absolutely LOVES me some subtlety. There is little as un-subtle as a punch in the face, right? Well, one can block and punch back, or one can move out of the way, then punch back, or one can move and punch at the same time (increasing difficulty according to Bruce in his book, eh...).
But, what about simply moving slightly sideways the instant before the punch is even launched, thus frying the visual perception of the aggressor, and mentally shifting his balance so that his unconscious tells him that he can't throw the punch at all as he'll miss and maybe fall down? Subtle! Definition of Aiki at work, again, in my opinion.
if you are not countering the use of force against you with a force, but using evasion to deal with said aggressive force, is that not aiki? If so, then I stand by my initial examples.