I know of one legal blogger who complains that certain copyright lawsuits really ought to be trademark suits (e.g., https://scrivenerserror.blogspot.com/2007/11/accio-lawsuit.h... , https://scrivenerserror.blogspot.com/2005/05/fan-fiction-tan... , https://scrivenerserror.blogspot.com/2005/05/fan-fiction-end... , https://scrivenerserror.blogspot.com/2005/05/fan-fiction-tan... ). But the courts generally play along and accept “copyright” suits that seem to be judged on trademark principles (but punished according to copyright law).