Also we see Schillinger probably end more promising young careers than he creates. He's basically produced (well not even then lmao) one prodigy while ending the lives of multiple people, along with their love of music, all for the sake of his own ego. And this one student basically proves by the end of the film he didn't need this teacher at all.

There's a scene in the later half of the film where we see the teacher playing piano at a jazz club and it's the most mid, low-effort elevator music possible. The film is pretty upfront about how much of a fuckup this guy is and how much of his "teaching" is him bullying people who are actually better than he is because it makes him feel like his life has meaning.