I might be splitting hairs, but couldn't this depend a little on how we look at it? If his overarching goal was to come into accord with kamisama, and this was a way of doing that couldn't we say the building of power was a means to this end? ...That the entire thrust of his actions (which includes the solo regimen) were about realizing a kind of Heaven on Earth?
Might it not be a fair suggestion that O Sensei was more concerned with realizing the purposes of kamisama than of building power? And that this is reflected in how he taught and allowed his students to then teach?
Well, I would seriously ask you to consider why someone with a supposedly purely religious ideal would pursue budo at all?
And that being said...why would he continuously explore, train in and continue to display demonstrations of POWER...all commensurate with the typical tests done in internal MARTIAL ARTS...if all he was really concerned about was God or The Gods?
I have no issue with a spiritual pursuit what so ever. In fact I think it is part of understanding or appreciating Aikido. It just isn't a source for power or aiki that the founder displayed and never was.
Why is it that no one, anywhere, who only pursued the spiritual practices, demonstrated ANY power whatsoever?
Because there is no power to be had from only pursuing a spiritual practice sans any physical training exercises. And for those who keep saying otherwise I repeat "Tell me who? and if it's you...step up, and let's test that out!" They won't because other than talk, they simply have nothing to show.
Again all of this conveniently avoids the fact that there was, and is a method to train for power that existed before him, he pointed to it, he practiced it continuously, and others who will simply do it will achieve similar results.
The second fact being most don't know it, can't practice it because they don't know what to practice and thus will NEVER achieve what he did to any degree.
They are practicing the art from the outside-in..instead of from inside-out.