I think the only thing you really can control is yourself, no one else. Self mastery is the heart of Budo.
I would re-word this slightly and say the only CONCERN we should have is control of self ultimately, as of course, any control we have over others is temporary and not really sustainable in the long term.
As far as budo is concerned, absolutely, primarily I think it is about learning self mastery, which is learning that we need to first be concerned about self than about others.
While this may seem a small thing, I think it is great actually. We need to understand in budo that we do, and can have power over others and at times we need to exercise this power, hopefully in a skillful way....otherwise we run the risk of turning what we do into a very narcissistic practice, which frankly I think happens alot in Aikido.