Well, good points, not that I disagree - I just think it can be an advantage when the inspired person is not the author himself, but things got sort of simplified, for lack of a better term, by a generation or two in between before someone wrote them down ....
Definitely a different time and circumstance. The Gospels in the New Testament were written, not as biographies, as much as for non-Palestinians. In some places, it is possible to capture the actual words Jesus used and retrace exactly what he did.
With Ueshiba, his words are in print, though sometimes overly symbolic or clouded in meaning.
Here are some of my hermeneutical thoughts:
Neither should be taken out of context as an historical beginning point.
Both should be given space for self contradiction and idea-growth as their lives unfolded.
Both should be given space for personal presuppositions and prejudices.
Of greatest value, as far as "trajectory" is concerned, we should try to keep clear their original intentions and then apply them to today's environment. We should accept limitations. They were quite human. And use the intention with care as we further it when the original intent is limited in scope.