I think the pattern remains. Armstrong was a fine performer. Gershwin was a composer. Different skill sets. Performance is a more right brained effort, composing is more left brained.
My personal, anecdotal experience is that I do better as a performer playing the trumpet than attempting to compose music. As a software engineer, I'm capable of composing thousands of lines of code in my head. It takes hours...sometimes days to get my fingertips to commit that code to actual files. I enjoy considerable ease in conceptualizing 3D structures and spinning them any way I desire in my head. That makes a variety of analytic tasks much easier. Eventually, that analog exercise on the right side of the brain needs to be expressed in a left brained manner to convert to a paycheck.
I have read that there is a correlation between mathematical and musical ability.