I'm the editor of Pseudopod, weekly horror fiction podcast, and have been reading horror fiction and watching horror movies and television since I was roughly 6 years old (watching, reading came a little later). If context is needed I will be 50 years old in a couple of days.

Like you, I have contrived a definition for myself as to the difference between "horror" and "dark fantasy" – mostly in the effort to feature more of the former than the latter on the podcast, as it is my personal feeling that a "too inclusive" approach to what constitutes horror, that folded in "dark fantasy" has led to a corrosive dilution of that genre brand starting in roughly the 1980s.

But I have to say I find your definition severely lacking. Needing to be "about the monster" is an extremely reductive and limited definition of horror as a genre in both fiction and film. "Don't Look Now" and "The Haunting", two of the greatest horror films ever made, are in no way "about the monsters", just off the top of my head.

If you are interested, my definition of the differences goes like this. Horror, in any format, in the whole is attempting to frighten, disturb or unnerve the audience. Dark Fantasy uses the tropes or figures of horror, but in its overall thrust is not intending to scare, but to achieve something else – whatever that may be and regardless of the use of the tropes and figures.