George S. Ledyard
As to Ikeda Sensei's work... Certainly a lot of what he is doing is straight out of what you, Dan, and Ark talk about. But quite a lot of what he is doing he got from Ushiro Kenji. I don't have enough familiarity with the range of what you and Dan do to say where you understand what Ushiro Sensei is doing. My experience so far is that physically you certainly do. But on an energetic level, I don't really know because I have not heard you guys talk about it. From my experience, much of the core if what Ushiro is doing has more to do with what Vladimir and Ryabko are doing in Systema than what the internal power guys I have encountered are doing.
This. It is a cardinal sin to assume that everyone who is effective is drawing from one wellspring. I feel that I have encountered multiple distinct sources of internal skills. Hell some of the sources I am working with have strategies so different from those described on Aikiweb that they do not even generate power. The people I have encountered with working skills are pulling from one or more of these sources, and undoubtedly from areas that I have yet to begin to penetrate. A lot of the people who are currently dabbling in these areas assume that the high level abilities are an individual's expression of a single skill, and worse, they assume that when they encounter someone who has working skills, those skills must be rooted in the same concepts they themselves are already practicing. Keeping one's mind open to the idea that you may not already be on the right track, that you may not even have a clue yet as to how someone's skills work, is the only way to create enough space in your practice to actually get traction in a new system. Of course time spent with anyone with working skills will help you get traction with other working systems, but please do not assume that they are definitely doing your stuff.