I don't think it's a mistake in principle, just in execution. They should have eased into it over time instead of cramming it all in at the beginning. Supernatural developed a similar depth of mythology and expansive cast over 15 years, not one episode. And they should have hired more professional-caliber actors and writers (wow, some of that dialogue is just horrible!).Yeah. If they had done Young Mary Campbell and her Scooby Gang, this might have been a better show. Shoving John and the Men of Letters into it was a mistake.