Steve
Mostly Harmless
I think you owe it to yourself to roll with an elite level BJJ black belt. It will blow your mind, my friend. Seriously. It's exactly what you describe. techniques become effortless when they are executed correctly. I've swept guys that weigh over 300 lbs effortlessly because I could feel the moment they committed their weight, just as you described.That would fit with one common definition of aiki. The definition I use is that it's where there isn't any resistance. Thus, when there is resistance, we're not doing "aiki" anymore - we're using other principles (leverage, structure, etc.). Those other principles are also used in aiki situations, as well, but are supplemented by finding that void where there isn't any resistance. That's why I say that resistance removes most aiki opportunities - where there's resistance, it's no longer "aiki" as I define it.
I have to admit I've never been happy with my ability to explain aiki in words. Students get it pretty quickly because they feel what an aiki technique does. They get to compare that to what I refer to as "Judo-style" techniques (usually the same techniques, just executed with emphasis on different areas).
The best I could explain it with something that I understand within your area, Steve, would be to talk about working against someone who has mount. If you go to bridge-and-roll (the term I know for it), that can be done against resistance by neutralizing their structure. In simple terms (so I don't get deeper than my own understanding), you can trap arms and bind them to you, using structure to prevent their knees from rising, lock their feet down with your hooks, and execute the technique. All of that can be done with timing, even against someone who resists, to some extent. Of course, if you are significantly stronger, you can go for whatever your favorite set of traps, etc. are to get them into position, muscling through their resistance. But you probably wouldn't. You'd probably go for whichever variation of the bridge-and-roll they'd set themselves up for, which would require the least muscling, and execute that one. That's what I refer to as "Judo style" (just to differentiate it from "aiki"). It's clean and efficient, and uses good mechanics and principles to get the job done.
The only difference between that and an aiki version of the same technique would be feeling the moment when they've committed some weight where they really shouldn't, when trapping the arm requires no real effort because they don't have structure already, and bridging will take almost no more force than it would without them there, because the trap leads them to start falling forward. And so on, until you end up with that super-easy bridge-and-roll, like they actually rolled off for you.
I've never experienced that with bridge-and-roll (I'm pretty workmanlike on the ground, and not very aiki), but skilled folks probably have. It's much easier to find when standing, because there are so many more ways to get people into it. A small shift in structure can take people way off their standing base. If it's done with good timing and feel, it leads right into the aiki versions of techniques. Of course, if they don't end up in a good place for the aiki version, we go to something else. It might be an aiki version of another technique (if they avoid one by pulling back, they probably walked into another), or it might be a non-aiki ("Judo-style") version of the original technique. Just like selecting the right response from under mount to escape, we have to select the right response for what they feed us when standing. Aiki techniques don't preclude the leverage/lead-based stuff, they supplement them.
A BJJ black belt, who also is a black belt in aikido, suggests (paraphrasing) that the difference between purple and brown is that a purple belt can identify these opportunities while a brown belt will begin to create them.