Christian - Since Ueshiba seemed to spend more time doing the Misogikai exercises, that Abe Sensei maintains (like funakogu-undo, chanting for long long periods of time, etc.), and stated that this was the key to his aikido - - - - - I tend to take him at his word. Tada Sensei, as quoted by Peter G., stated the same thing, but also stated that Osensei didn't (at least after the war, I interpolate), tell people to do these things and expected people to supplement or find such information on their own. Which leads to Peter G.'s latest column on Transmission, I think.
I have a friend, who is a pure grappler - dare I use the term, MMA - who has always found aikido utterly bewildering. He asked me recently, "So this guy Ueshiba was really supposed to be "the man," right? How could he be that doing that aikido stuff?" I got up and said, "Well, he used to to this kind of stuff for hours a day," and started doing funakogu, first slow and then with some relaxation to "pop." He watched, nodded sagely and said, "Oh, I get it. Core strength training."