Well I got that. I see it as directly relevant. I was suggesting that it may not have ever been a deviation or departure ..from...aiki...until later. I question whether the source came from a deeper understanding that has been lost as I can see direct relevance...to aiki.
Okay, then you're going to have to explain this to me. Here's the situation: Shidachi is in a strong chudan stance; no suki. Uchidachi is a in a strong chudan stance; no suki. The situation is a stalemate. This is "aiki", as in "kisetsu ga au". Per the kata, shidachi drops his strong chudan stance, to invite uchidachi's attack, or any kind of response, and create a suki. This is called "departing from aiki". Breaking the stalemate. This is the use of the term "aiki" in YSR, and the use that Mr. Shishida is talking about.
I'm not saying the body skills now popularly known as aiki did not exist in these old arts. I think they did and do exist; I believe they are in Yagyu Shinkage-ryu. However, I don't believe the use of the term "aiki" above refers to them. I have to side with Mr. Shishida in the idea that the term was used differently at that time, and different terms were used to refer to the body skills. But I am honestly open to persuasion. If you can explain to me how the above situation is directly related to the body structure and skills used in aiki arts, I'll happily revisit my position.