These things are the composition equivalent of Guitar Hero...

They give users (players?) a sense of agency, making it satisfying. But in reality, you're no more composing than a guitar-hero player is playing the guitar, and nor will you learn how to from doing so. No matter how sophisticated the transformations in an LLM, you're ultimately using other people's music in a sophisticated mashup game.

However, in guitar hero, the people's who's music was being used at least got royalties. :-/