I'm curious why O'Sensei became a Japanese National Hero, and I haven't heard the same of Takeda.
In my opinion, the message of the Founder (as it was perceived anyway) gave him and his art an appeal that spoke to people all over the world. If it had just been about technical sophistication, there would have been far more "household names". There were certainly a number of people whose "aiki" was as good, or even perhaps better.
We know so much more now than we did when i started Aikido. Stan Pranin almost single-handedly lifted Daito Ryu out of relative obscurity using his magazine, Aikido Journal, to spread awareness of the art, its history, and the surviving exponents.
In terms of modern Japanese, and even Korean martial arts, it would be hard to over estimate the influence of Takeda and Daito Ryu. Many of the top martial artists of his day trained with him for some period of time. Ueshiba and Aikido are only the best known of these. Hakko Ryu, Shorinji Kempo, Hapkido, Yanagi Ryu, etc all were influenced by Takeda and Daito Ryu.
But most of these styles are relatively unknown outside of Japan, some are obscure even in their homelands. Whereas, Aikido is one of the best known and widely dispersed martial arts, perhaps the most popular of the non-sport martial arts.
I can only attribute this to two factors... First, Aikido has an aesthetic which more practically oriented martial arts do not have. While the impractical nature of Aikido movements may be a source of criticism by some, I think it is a main source of appeal for many of the art's practitioners.
Second, the message of the Founder, no matter how bowdlerized by his successors, spoke to thousands of people on a very deep level. This may have been less true in Japan but it was certainly true overseas. Teachers like Mary Heiny Sensei have told me that it was this precisely which attracted them to the art. The figure of the Founder himself was tremendously inspiring. The man clearly had a kind of charisma to attract and hold so many strong personalities.
I think it is different now. You can see it on the forums... When I came out of school it was the the tale end of the Hippy days. We all grew up on Joseph Campbell telling us to follow our bliss. We didn't see anything strange about deciding to devote our lives to an art with no commercial potential. Of the people in my first dojo in DC back in 1976, at least five have become senior teachers. Of my second dojo in Seattle under Mary Heiny, at least six have gone the distance. Of all these people, I would say that the person of the Founder and our perception of his message was central to all but one or two.
Yet now, most of the young men seem to want only to fight. They want to do what they see on prime time cable. Movies like Fight Club spoke to this generation, not messages of peace and harmony as it did to ours. My generation had Woodstock without a single act of violence amidst a half million people. At Woodstock II they tore the place apart. I see the average age in most of the dojos I teach at rising significantly. We just don't have the young folks coming along like we did 15 years ago.
Anyway, that's why O-Sensei was famous in a way that others were not. His message was broader by far, it spoke to people all over the world in many different cultures. I don't think that any art or teacher, no matter how sophisticated or effective could ever match the appeal of an art with a great idea behind it.