Let me ask a dumb question. If O Sensei intended to be understood (let us assume this is so, since he troubled to lecture and to write the Doka) and native and scholarly Japanese speakers have trouble grasping categorically what he meant -- then do we not have to ask the question if his language and intent was precisely outside of category in many respects -- of Japanese or any other language? This may make it less accessible in some respects, but more accessible without regard to strict language in another sense. Image and intimation speaks more than any category. On empirical grounds his communication mode has some demonstrated merit, whether it was a deliberately chosen or simply fortuitous strategy.
IMO, it is all a question of idiom and context. Ueshiba was a man educated pre-war, working within a very specialized cosmology, and describing with words what has long been referred to in budo circles as "that which cannot be described with words." Naturally, it's very, very difficult to reach an understanding of what he was saying without an idea of his particular context and idiom.
This issue is hardly unique to aikido. In a series of lectures on budo in general, and kenjutsu in particular, Yagyu Toshinaga described this problem with the terms "hontai" 本体 - the essential form, and the "hongen" 本源 - the essential source of martial arts.
The form is in the physical practice, be it kata or conditioning exercises. The source is the theoretical framework on which the form is built. Without the form, the theory is nothing. Without the source, the form is empty, just a house of cards. The budo have used a variety of philosophies to structure their theory. For some it was Buddhism, Zen or Mikkyo, for others it was Shinto, for Kano it was early western kineseology, for Ueshiba it was Omoto. But the theory is not self-sustaining. It requires the physical practice for understanding.
For example, of late I've been reading Heiho Kadensho
, a treatise on the martial arts (Shinkage-ryu in specific) written by Yagyu Munenori in the early 1600s. The edition was prepared by Watanabe Ichiro, a respected historian specializing in budo. It's been commented on by Imamura Yoshio, another budo historian who's specialized in the Yagyu family. Although both have done tremendous work in reading, interpreting, and preparing these kinds of documents for publication, they both shoot wide of the mark on several key points, simply because they aren't interpreting the documents back through the physical process, as was intended, nor were they given the oral teachings that decoded some of the written material.
I think Ueshiba, like Yagyu Munenori, intended to be understood, but only by those who had put in the work to reach the physical understanding that he had.
If there's one thing I think Professor Goldsbury's columns here have made abundantly clear, Ueshiba was not operating with the intention of cogently taking his students from point A to point Z. Rather, he gave them his understanding of the system of the world, and he expected them to put in the physical work to illuminate that understanding.
So naturally, to truly understand Ueshiba's words, one needs to understand his context, physical and metaphysical. That would require a study of the things he studied, the way he studied them. It would require the mat time, as both sides inform the other.
I do not say that this is all necessary to do aikido (although a case could be made that it is in order to do "Ueshiba's aikido"), but I think it is necessary to understand how and what he wrote about aikido.