Re: that ^ sentence: Yes, yes, and yes. 100%.
As far as your comparison, I've never thought about Duke's sound in relation to Shepp, in particular. But I have wondered if Ellington hasn't gotten his due with regards to bringing an "African musical vision" into jazz -- way, way, way before the idea became fairly common in the 1970s. ... Which might be another way of saying the same thing that you're suggesting.
In other words, if you have a different vision (and different values), you'll produce a different sort of music. And traditional European ways of thinking about Duke's music aren't adequate to the task -- and perhaps miss the point entirely.
The fact that Duke was an autodidact also comes into play here. It's part of the mix as well, I think.