It's not that uncommon for professional programmers to be pro-level musical soloists on the side, or for retired programmers to play top-level music. The reverse is far less common. I do think that says something.
> Anything as competitive as an artistic field will always result in amounts of mastery needed at the top level that are barely noticeable to outside observers.
Sure. Top-level artistic fields are well into the diminishing returns level, whereas programming is still at the level where even a lot of professional programmers are not just bad, but obviously bad in a way that even non-programmers can understand.
Even in the easiest fields, you can always find something to compete on (e.g. the existence of serious competitive rubik's cube doesn't mean solving a rubik's cube is hard). A difficult field is one where the difference between the top and the middle is obvious to an outsider.