@lispi314 @yassie_j @mmasnick @ami_angelwings I think a slightly better example about copyright would be more like Vocaloid and more recently Vtubers, which entirely higes on fan works, and latter effectively created a new industry. (Could likely also say the same thing for Minecraft, the most sold video game, which to me would be a forgotten game without let's plays, tutorials, …)

Meanwhile fiction works are kind of strange to have information on because most fiction websites don't have things like number of readers and a lot of it is entirely non-commercial or at best self-published and so hard to aggregate.
Like I don't think anybody can know how many copies of touhou fanworks have been sold.