Well, I can't comment on a question unless you ask it - and you say that you don't really know what Aikido is, so I'm not sure what you're asking...
Maybe that's a difference in concept with Morihei Ueshiba.
So in your view, Nishio, Saito and Yamaguchi all practiced different martial arts?
Here's the deal, I genuinely don't know what makes Aikido Aikido. Here's my working definition, "Japanese Martial art based on the teachings of Morihei Ueshiba based on the technical syllabus of Daito Ryu." I can't put any more specifics on it than that because, as you kind of point out with your sample Sensei, it varies so incredibly much after that. The only thread I can find is a general similarity in techniques and a cult of personality around the founder. If Aikido is supposed to create a golden bridge, then it's failed. There are more people doing aikido now than ever before, and the world is no better off. Tensions are rising between cultures. If it's supposed to make you a better person, why are so many of the senior shihan so despicable? Womanizers, alcoholics, abusive to their students. One minute someone is the shining light of aikido, writing books about the deep moral lessons of the art, then it comes out that he's been sleeping with underage students, or maybe just 1/2 of the women in his own dojo. Perhaps it's a physical metaphor for conflict resolution (this is a very popular view here in the NW). Why then are there so many organizations? Peter Goldsbury has even stated that in his view (and I'm paraphrasing) that the nature of aikido (at least in Japan) does not even really allow for a resolution of conflict between members of the same organization. Bernie Lau has talked about how his teachers in Hawaii settled some of their differences, they locked the door to the dojo and punched and kicked each other until one cried unkle. If the ideas presented in books and lectures like the ones you bring up are so central to the art that they could be approached without ever doing the physical side of aikido practice, why have they been nearly completely dropped by the Aikikai?
So I'll again turn the questions around to you, "What is Aikido?" Would you say that Nishio, Yamaguchi and Saito are all doing Aikido, and if so, what is the common thread that makes aikido unique and distinct from other martial practices?