Re: Sumo: light vs heavy and IS?
I'm paraphrasing something Ark said a few years back along with some comments of my own which I think apply.
Budo is like a religion: the practitioner takes some mental construct, a set of principles, and keeps those in mind as an ideal, and then goes through stylized moves that allow him or her to feel as though they are putting those ideals into physical motion and instilling discipline in themselves (budo is intended for social benefit). With that there is some exercise for the body. However, no great development of the body ever happens, nor detailed understanding of it; ergo, the understanding people find from doing budo is really not very deep at all. This is Shin(mind) gi (technique) tai (body) in the order expressed in the phrase.
Someone could take on aikido as a form of gyo, or asthetic exercise, but I haven't seen much explicit instruction of that nature in any dojo I have trained.
On the other hand, studying "aiki" along the lines of bujutsu follows tai(body) gi (technique) shin(mind), exactly the opposite: the practitioner forces his or her body to undergo specific exercises that change the body and give him or her some deep understanding of the body, to great detail. This leads to an understanding of the principles. As that understanding develops, the body can be used to perform so-called techniques (which are not really special movements, but only the body in motion according with the understanding given the practitioner), and finally, when the practitioner is really powerful, he or she may decide to no hurt or harm an opponent and use the training as a kind of ascetic exercise.