Agreed on the Anime front. And that most horror writers are better at short lengths, although I'd argue that Lovecraft was best in the modern Novelette range, and his Novellas/short novels Charles Dexter Ward and Mountains of Madness are classics, but the point stands.
Still, these don't make up for the unfilmability of horror, for me at least. It's hard not to show a monster in a movie without it coming off as cheesy, but almost anything you show cannot live up to a reader's imagination. It's even harder to show the unexplainable weirdness in a story like The Music of Erich Zann or The Willows. I just don't think you could make movies of those stories without it coming across as cheap effects or unexplainable weirdness. Worse, written/spoken fiction is inherently better at showing the state of mind and inner dialogue of characters, while film must rely more on actions and spoken dialogue. I think that makes it hard to really show a person going mad in more subtle ways. For that matter, ambiguity is usually reduced and it seems hard to do slightly unreliable narrators. Either nearly everything is a hallucination of the narrator, or it is all accurate, you seldom see the little shiftings of truth in film. And some things are much much better left ambiguous in a way that images are not. I can't really imagine The Repairer of Reputations in film, for example.
{Although, I'm just reminded of a very good example of this I saw the other day, the Adventure Time episode "BMO Noir".}
On the topic of writers who don't read, I have no trouble believing it, it's depressing, but I'd also think it is the kind of thing you could discern from someone else's work. Maybe I'm just being a snob, but I assume that any writer who hasn't read much of anything is not one who will impress me. Then again, I'm in the minority that loves Ramsey Campbell and hates Stephen King, so I probably have no bearing on commercial success even if I'm not full of shit about being able to tell.