Ueshiba's aiki came from Sokaku Takeda...
Didn't Ueshiba mostly credit Sokaku with "opening his eyes?"
Even more contemporarily, there are people on these Internet pages, myself included, who have trained both in Daito-ryu aiki/IP and in their Chinese equivalent, in my case I Liq Chuan. I can state quite frankly that they are... the same animal.
And while there of course is such thing as simultaneous and synchronous invention of things in different places, such as the printing press and, possibly, the wheel, something as complex, nuanced and sophisticated as an internal body method is very, very unlikely to be something that two different peoples could event, identically, without any cross-pollination of ideas.
I think the "cross-pollination of ideas" could be looked at in a more general way. What was there around in the environment? Well, everyone is basically built the same. People have a head, torso, two arms, two legs, ten fingers, ten toes, and stand upright. The people who "discovered" these arts also had natural phenomena and forces around them: fire, lightening, wind, water, sky, earth.. And also natural elements such as trees, animals, insects, etc..
It's not too far of a stretch to think that the playing field that all people are on - regardless of their culture - is, ultimately, the same field. And for those who would delve deeper into studies such as movement, strategy, integration, would come out with similar conclusions.
The idea of "Hidden in Plain Sight" is even simpler that what sensei might have said or taught to another, or what culture might have copped from another. The "plain sight" part reveals that anyone of us has direct access to the very forces, elements, and designs that Ueshiba or anyone else would have.
Didn't Ueshiba say that the reason most of even his students weren't "getting it" was because they didn't understand in/yo. And if "yo" could represent what Ueshiba actually did say and did do, then "in" could represent everything he didn't say and didn't do.
To read esoteric texts seems to have a common denominator in that it can act as a sort of alarm clock to wake us up. It's not so much what the texts say. Like Cady pointed out with the "same animal" found in various arts, so there's also the same animal that seems to appear over and over in writings from various cultures and teachers.
I think I probably wound up getting my first taste of the "deep end" by reading Huna texts. Also various shamanic writings. But regardless of whether it's something out of the New Testament, Bhagavad Gita, Sun Tzu and whether the culture is Chinese, Japanese, Indonesian, etc.. there's always that same animal.
Ueshiba certainly had to have had his nose in Chinese writings. But it seems that it's the level of consciousness that would, or could, have come from those writings that would have acted as a sort of regular nutrition for a higher-level of fuel to allow him to see deeper into the natural order of things. Including non other the "the universe" - because, apparently, he realized he was the universe. Another one of those "same animals."
The same animal appears to be universal. "I am the universe." is quite a stretch from an identity of "I am Chinese." J. Krishnamurti gives some good insight - and another one of those same-animal alarm clocks - about nationalism equalling violence. And also.. "There are the states of inattention and of attention. When you are completely giving your mind, your heart, your nerves, everything you have, to attend, then the old habits, the mechanical responses, do not enter into it, thought does not come into it at all."
Being attentive and conscious. That would have been that same animal that was the catalyst that Sokaku gave to Ueshiba. Sokaku was the initial alarm clock for Ueshiba to open his eyes. To wake up. To loosen the mechanical responses. That was a big theme of Gurdjieff, Ouspensky and many other western esoterists. Jesus said, apparently, "For those who have ears to hear and eyes to see."
Same animal. Woof.