Someone has to be in charge of genre definitions. And if you read what I’ve posted, I listed publishers, writers, readers, and reviewers. Not just publishers. The industry is more than just the people who publish writer’s works.
Yes, a romance is the old name for adventure fiction. All of Jules Verne and H.G. Wells are technically romances by the definition of the day. Today they are science fiction. Just as the Barsoom series were Planetary Romance in their day are are not science fiction. The term science fiction for the genre came into being in 1926 with the publication of Amazing Stories. If you read through the stories today, you might think it was some other genre. But that is the origin of science fiction and many sub-genres carry on with the fanciful imaginings that filled the pages back then. This was one of the magazines that Isaac Asimov grew up on and then submitted stories to. The early years feature names modern readers don’t recognize, but when you get into the late 30’s and 40’s, the names become more familiar. You don’t get magazines dedicated to publishing fantasy until after WWII. The Hobbit was considered a children’s book and The Lord of the Rings was when they first realized it might be more. Before that you have plenty of what are called High Fantasys. Tales of Merlin and things of that sort. David Eddings was the last big name I heard of in that sub-genre.
But when you really look at the books the get published (because, let’s face it, there aren’t that many movies or TV shows in either SF or fantasy), there is a distinct difference between science fiction (primarily space opera) that edges a bit too soft and fantasy that tries to be realistic. Song of Fire and Ice is probably the series with the least amount of magic and based on real history (the War of the Roses) that I have encountered in recent years. Tolkien tended to lean to mythology (specifically Anglo-Saxon, Norse, and Finnish) and also kept magic to a minimum… most of the time. But he is the father of the different races that has been so prevalent in many later works, like Brooks.
If you read and study the genres, it is pretty clear what is what. In general, stories with a high technology setting with space travel or computers are science fiction. Stories with a medieval setting with magic and royalty are fantasy. There isn’t much cross over and when it is it is very clear which genre it belongs in. See, in a fantasy setting, the magic isn’t just one or two characters. It permeates the world. It dictates the plot. The Hobbit is driven by a dragon and a magical crystal. Gandalf doesn’t lend too much help. The Lord of the Rings is driven by the one ring. In both you have magical creatures, both good and evil. Brooks copied that and made the magic even more pervasive. In science fiction you can feel technology dominate the story. Technobabble and faux terms and hightech names. As Mark, Carrie, and Harrison have said, normal people don’t talk like that. Yes, the force is key to the story, but it is the tech and the war the drives the story. It is the death star and destroying it that the first movie is about. The force is there and it is part of Luke’s journey, but it isn’t the be all and end all of the OT. The rebellion is. The rebellion succeeds because Luke beheads the empire with his actions. But his actions are not governed by the force, but by human emotions. Magic does not win the day like it does in fantasy. Even LOTR, where Frodo destroys the ring, it is still the ring being destroyed that wins the day. In the end he could not do it and it took Gollum to do it for him. But in Star Wars Luke and Anakin take the actions that win the day. That is very science fiction.