Re: aikido and sword principles
My take on this is that people actually learn on every level, but they tend to focus on learning from a methodology they alrady trust. So, for instance, I perfer a more scientific approach to developing my aikido in term of physical practice. My friend, prefers a more phylosophical apprach to developing their aikido. We both need both ways, but we tend to focus on what we trust more.
If O-sensei got some understanding of how to hold his body in the most effective way from sword movements, then he would trust that, and probably prefer to teach in that way as well. I don't actaully think you need an excellent sword teacher to learn aikido - which is probably considered blasphemy by some. But, I do think you would then need some other extra-exercises to develop what is needed. Luckily, some people have developed to a decent understanding with and without auxillary sword practice, so there is a choice for students to focus on what they think might help them most.
Also, please remember that what is typically seen in aikido as far as sword training goes is not generally considered real sword work. Even Saotome sensei who IS probably a sword master, wouldn't say that someone who learned the sword kata in his system knows very much about real swordwork.
The good news, is that if you just don't have enough sempai around, you can get a lot out of swinging your sword in every direction - especially if you do it so much that you can no longer use "normal" strength to continue to make powerful cuts.