I think there is not so much music in the pentatonic that is formed by the black keys, or a related scale. Depending how strictly you’re using “pentatonic” the

I think there is not so much music in the pentatonic that is formed by the black keys, or a related scale. Depending how strictly you’re using “pentatonic” there, I don’t think you’re correct, unless I’m misunderstanding. In the wider classical and jazz repertoire there’s plenty of music written in Eb, Gb etc, heavy on the black notes. For example, Debussy’s piano music often uses keys with lots of flats (or lots of sharps). Chopin supposedly played the black keys with his thumbs in some cases, against the accepted style at the time. In jazz, Billy Strayhorn (who I think was strongly influenced by Debussy) seemed to be very fond of writing in Db.