The only element that would make me hesitate to call "I, tonya" as a vanity project is because Margot Robbie while a rising star, Margot does not greenlight movies just because it's her. The studio probably greenlight it cause they thought it had the chance to be an Oscar contender so it became a hot property. A vanity project is usually something even the studio doesn't want to make and they'll go alright we'll do this to satisfy that dude and cause they have a deal with him/her.