Fascinating! I'd love to know more about your work.
Here's the big unanswered question, however: I think the 80-90% thing can be applied to the mechanics of moving the hands, learning the notes, etc. -- the things involved in playing an instrument.
Based only on my own experience (and I realize that one cannot generalize which is why I'm asking, and not claiming to be a fount of knowledge), playing an instrument and composing music are different talents, even though both deal with music. Moreover, I'm not sure composing music can even be done to a professional degree without a larger dose of the nature stuff than is necessary in learning an instrument.
I'm certain that learning those mechanics (or indeed music theory) doesn't make a person able to create a decent melody. Even Rimsky-Korsakov, who wrote a seminal work on orchestration said in the introduction to the book (I'm paraphrasing), "I can teach you to orchestrate. No one can teach you to compose."
I will grant that the more I create, the more easily the ideas come, but it's something entirely different from being good at playing non-original music on guitar or piano, which I also do professionally.
There's something different at work there having little to do with instrumental skills.
Something happens inside my head when I compose. I'm not even conscious of it; seems like it just happens.