another reason that fanfic will never be on equal ground as real books, is that all the heavy lifting has already been done for them. the world intro, establishing the rules, characters and their introductions, all the plot points and themes, all of that happens in the books (even if it's done somewhat badly and maybe clumsy, it's still a world someone created). fanfic writers don't have to worry about how to explain the magic/power system to their audience, bcs the audience already knows that!
Also, due to that reason, almost every sentence and paragraph written in a book has much more weight to it than in a fanfic, since the book is (almost) always trying to tell us something. Im not saying that all books are like that, but the wors chosen to describe anything in a book are always chosen for a reason. Meanwhile it feels as if words in a fanfic are used more flippantly, without much reason but behind them. (idk if this is true for all books either, but it's just something i picked up on while reading a new book i got, how different the writing is in a book that's trying to establish the rules and characters and the world- compared to a fanfic that already has all the work done for it.)