....This notion of "harmony" that you posit I think has a lot more to do with "cooperation" . .
As an aside, back a good decade and more ago, I had the opportunity to hang around and observe Rickson Gracie a fair amount, for a while. I watched him teach, train, and roll (grapple.) He was doing something that almost no one else I have ever seen in BJJ really does. Totally effortless, flowing, really amazing stuff. Shocking at times in fact, how easy it was for him. I would definitely call it Aiki in a practical sense. He wasn't manifesting "everything" that one might classify as "internal Aiki skills" but his ability to use the other person's intention, movement, and in essence, energy, was phenomenal. So, somebody out there, at least, has some sense of deeper skills and their application.
Similarly though to what some are pointing to in Aikido, most BJJ practitioners are not doing what he is doing, nor do they necessarily know that that level of skill etc. exists.
One thing he used to say, and this was not a mis-translation on his part, was "flow with the go" as opposed to the conventional phrase. I liked that a lot.