It was his use of it to infuse an entire art and refine it as a body method that was dramatically different in his era.
OK, I don't have a quarrel with Takeda "infusing an entire art (and offshoot, if you count Ueshiba's "Aikido"), but my point was that the "body method" was not "dramatically different in his era". We know that what you're calling "ai ki" (Hua jin and variations) was available in China and, *from the few indicators that westerners have today* (Like the few books in English and now, increasingly, textual sources like the ones Ellis used in HIPS), was undoubtedly available to some degree in Japan in a few arts.
I was reading a monograph by Donn Draeger on Kiai and while I was listening to what he was saying about some of the Japanese watching invited Chinese perform (how did they know to invite the Chinese for these things if the Japanese weren't aware of them?), I noted the possibility that a number of the Japanese probably knew what was going on, but since Draeger hadn't been told all the secrets he thought he was unique in commenting on them. Same thing here..... just because there's not a lot of written documents available about what were secret techniques (like Takeda's "aiki"), it's not a good assumption that only Takeda had this information. On the contrary, even E.J. Harrison's acquaintance Nobuyuki Kunishige seemed pretty aware of a lot of the ki/kokyu skills and even "grounding" is a rudimentary usage of "aiki".