I think that's a real over-simplification - Ueshiba spoke about Takemusu quite a bit in "Takemusu Aiki", and it gets quite a bit more involved than that, but that's probably another, longer, discussion.
Fire it up, please.
He certainly did take things from various places and made them his own, but there's no denying that he really only studied one art seriously, was only really licensed to teach in one art, only issued certificates in one art other than his own, an art in which virtually all Aikido technique can be found - Daito-ryu.
Ignoring that as if all these different arts had an equal influence is somewhat misleading, IMO
What does "studied one art seriously" mean? And does "recorded" history give any kind of accurate picture? Ueshiba could have been waiting on a train somewhere and met some old dude or cute girl, and have gotten as much or more out of that interaction than anything he got from Takeda. How do we know? I wouldn't even include what Ueshiba "studied" with Takeda as "serious." Not in terms of where Ueshiba really progressed and came into his own, and what we can see developed into at least Aiki Budo. That was Ueshiba's "ri" - during which Onisaburo was heavily around.
Look at Miles Davis' education. He went to Juilliard for a bit. Do we figure that because he didn't have a "formal" education with all the rank and file degrees, that he wasn't serious? And when he got really serious, he started hanging out at an apartment in Harlem with Charlie Parker and Dizzy Gillespie. And bebop was the shu education Miles Davis received. His ri stage saw him moving more into Cool Jazz. Look at post-war aikido as a softer more expressive version of Bebop, which came out of Swing. Same thing, same exact time period.
Do we determine Einstein's "serious study" by academic records? I wouldn't. Einstein did his "serious" work hanging out zoning on the couch, and making love to his wife, Mileva Maric, and their magical discussions. He was studying her ass. That's where his genius came alive. Not in any school. Einstein continuously blasted the educational system in Germany.
Takeda was the "shu" stage, and some of the "ha." Fine. It's a form. So what. You start digging around in DR, and you're going to run into CMA, and their core Taoist sciences, pretty fast. And the DR "form" doesn't teach that much. DR and Aikido do appear similar, and most version will get you to "shu." You try to even move into "ha" around aikido, and you'll run into problems. A lot of aikidoka who manage to get to ha, and then to ri, will find themselves going where the goods are, CMA.
Japan is a small country. They have longed looked outside and brought in "the goods" and repackaged them - often as their own, giving little to no credit to the source. Look at automotive design and engineering last decade. Yes, there were Toyotas, Nissans, Mitsubishi, etc.. And they make good, decent, dependable cars. But if you want to look at the "source" of what those companies did, you'll have to go to Germany for the engineering (at BMW), and to their American designer, Chris Bangle, and to the American company that made the software that all car companies use, Microsoft. The "source" for the original car that was THE mold for cars made last decade was the BMW 7 Series. Japan grabbed it, saw a market, and ran with it.
If you look at BMW now, since Chris Bangle left in '08, BMW has been looking to Japanese companies for inspiration. Jump in a BMW in the last few years, and you'd swear you're in a Lexus. Drive a '06-'07 750i, when BMW was really entering the sweet spot of the design and production of the 7 Series, and you understand the major impact that car had.
It's interesting, because this "stuff" this "spirit" seems to blow around the globe. The Germans will have it for awhile, make some innovations and then fizzle out. Make a mess. Clean it up. Rinse and repeat. Same with US, Japan, China, UK, and Russia - the major world players. And then it'll blow around to whomever's turn it is, and the fun is on again.
So, where's the excitement in aikido today? Where's the innovation? The heirloom seeds? Where's the spirit? Who are the voices and the people who will influence and offer leadership in the coming next 10+ years, as the torch of one generation is passed - or taken - from the preceding one?
Great thing about heirlooms. None of them look alike. In fact, they're pretty funny looking. Not uniform at all. But you get a taste of one...and you remember. Even Shoji Nishio would say, "You already know this, I'm just reminding you." I heard this directly from his mouth. Not from some book I've read. I don't even know if there's a record of him saying this anywhere. It was the single most important transmission
of information I've ever received concerning aikido and martial arts. Something along the lines of what you might call a seed.