As a counterpoint, Bartok’s Mikrokosmos [1] was the “textbook” for a piano sight reading class at my community college. He does have a lot of accessible, even pedagogical, pieces.

[1] https://en.m.wikipedia.org/wiki/Mikrokosmos_(Bart%C3%B3k)

I mean, Bartók is really not that random: polytonality, pentatonic and octatonic stuff, whole-tone scales etc. are all things you can practice and put into work in his music. (You can argue that Schönberg is even less random, cause serialism, but that probably doesn't help too much when playing the piano).