I think we may all be saying essentially the same thing, but missing the interceptive threads...Sean, all the Shihan you mentioned did indeed create their "own" Aikido, but, to my knowledge, not one of them did so until they had so selflessly and completely pursued the art directly under O'Sensei, that they came up with something, a true creation, only after this period of discipleship. (See the history of Saito Sensei during the Iwama years). Read Chiba Sensei's account of his being in the next room to O'Sensei as his otomo, sensitive enough to know when O'Sensei would waken...
I think this may be ultimately Eugene's point (Eugene, please correct me if I'm wrong). I think what he's responding to, and I happen to agree with him, is that there is a pathway of traditional study - Shu-ha-ri. Ri, the period of one's training when one breaks from one's master to create something unique, an expression of one's "own," comes only after Shu, and ha - stages of so completely emulating one's master (and, again, emptying one's own notion of how things should be)that one's vessel, one's receptor of training, is clean, and can then take anything and make it one's own. This process cannot be circumvented if one is to train in a traditional manner. And I agree with Eugene, if I am reading him right, that this process is the only way to preserve budo via isshin-den-shin, mind transmission, for future generations.