the story is set in an isolated community that has a very long unbroken indiginous pagan tradition

Maybe that was how it was in the book, but definitely not in the film, which makes it clear that the whole pagan thing on the island is a recent bit of English folk revivalism foisted on the Scottish locals by the landlord, with nothing to do with whatever indigenous pagan traditions might have existed previously. That's what made it all so daft.

If you want to find seriously scary pagan community these days, I'd think that the States would be a much more plausible place to look than Scotland. I imagine that one reason for switching the action across the AStlantic might even have been to make it easier for filmgoers to believe in the story and find it scary.