If I host a song I don't have license to on my website I'm violating copyright by distributing it to you when you listen on my site.

If my parrot recites your song after hearing it and I record that and upload to YouTube. I've violated your copyright.

If a big company does the same(runs the song through a non-human process, then sells the output) I believe they're blatantly infringing copyright.

Big Company is not distributing the input images by distributing the neural network. There is no way to extract even a single input image out of a diffusion model.

I should have specified the OP has legal rights to the song and the end user listening was under the same granted/implied license as a program doing the web harvesting, my bad.