I see you updated your initial comment to replace Piano Man with The Entertainer (or at least, I don't remember seeing the latter there before). I'm not sure I like it better than the Weird Al song, but it could give it a run for its money. (I wouldn't answer Piano Man, which is a song I live, only because IMO it's not "about the music industry" enough.)
Rounding out my list would be Sell Out by Reel Big Fish, The Load-Out/Stay by Jackson Browne (if it doesn't have the same problem as Piano Man), and Life’s Been Good to Me So Far by Joe Walsh. That last one is not because I particularly like it, but because it's the only one that came to mind without having to read other people's answers.
I did add it, before I started editing in links. I never had Piano Man on there, which is definitely about the performance life but not about the industry.
Of the ones I listed, "Radio" and "The Entertainer" are definitely the most critical of the industry.