One concept that I hear of with regard to Chinese internal arts is solo training. That would seem to be a consistent methodology. If that is a hallmark of Chinese training there is a problem because Takeda didn't teach solo training to any of his students.
OK now the argument is more clear to me. What is the reason to say that Takeda did not show solo methods to a few students (I'm thinking, Kodo, Hisa, Ueshiba, Sagawa)? By inference I think it looks more like he did show some. So these are the specific points of the argument I guess:
1. Did Takeda have solo training methods (a general strategy, as well as specific drills) that created a "core skill" that was of central importance in manifesting aiki?
2. DId Ueshiba also have such a method?
3. Did Ueshiba glean any of that method (training strategy, or specific drills as well) from Takeda?
4. Is such a core skill (and its training methods) something that comes from way back and is thus extant here and there in other arts? (And extinct here and there in different lineages of the same arts, as well)
Cliff, you've read HIPS more than me I guess so I am not going to pontificate. But since there are shared results (peoples' demos and explanations of their arts), parsimony alone suggests that these arts of closely related cultures have shared methods (though you seem to have not liked that argument in this thread). There are specific evidences for 1, 2, and 3 above as well, and I think Ellis' writings are pretty targetted and detailed regarding those. (And Ueshiba's comment that DR has "a great training method" comes to mind, as well as the sudden appearance of solo spear training in Ayabe as to point #3 above.) So the question becomes, do we think the solo methods of Ueshiba are very different from those of Chinese arts, or should we consider all these methods as related attempts to build the same internal "stuffs?"
Again, it mostly comes down to what methodologies one will choose to investigate for oneself -- otherwise this is mostly an academic interest. But to be clear, it sounds like the argument is:
Is "aiki" as expressed in budo (aikido) something unique to aikido or to DR?
Is it just another example of martial artists manifesting a traditional power called "nei jin" amongst combat arts which are known to share cultural ties? (Both horizontal and vertical cultural ties)
Considering similarity of results (evidenced in demos and explanations), and known cultural ties, and what I have experienced as congruent strategies, I personally go with the latter.