One thing I would disagree with is that only outliers, in the sense of rebels like Takeda or Ueshiba can achieve mastery, although looking at Japanese matial arts from a modern perspective, it's understandable that it appears that way.
One problem we have is that koryu, itself, is an anomaly. Sort of like "classical music." In Beethoven's heyday, each and every classical musician was an "outlier" in the sense that what they composed was new - and, improvisation was part of what was expected. There is a wonderful account of Hummel (a wonderful composer overshadowed by Beethoven) at a party. A brass band happened to march past the window, bleating out a tune, and Hummel improved waltzes, for hours, on that single tune, as the young people danced the night away. The last great musician of this type, Earl Wild
, just died in January.
Similarly, when it wasn't "koryu," but 'living ryu," there was a) a place for improvisation within a ryu and a break-out failsafe if one improvised beyond the bounds of the ryu b) Properly executed, an authentic ryu had a built-in mechanism towards mastery within it. For me, one of the most remarkable things about martial ryu is there is, within one, an "outlier formula."