I hadn't heard the postulate "one being that the more one writes, the less remarkable one’s work is apt to be" before. I suppose that outside the world of the literary criticism, there's a bit of an opposite feeling: If you're great, you probably have a reasonably large body of work.

A while back, a friend and I both bought a copy of the complete works of Lovecraft; a single volume. It's a pretty thick book, but I was surprised it was just one book. For all the influence he had, all the diverse tales of horror, it all fit in one volume... with a reasonably large font-size at that. I remarked to my friend about this. Call him influential, but I'm not sure I'd call Lovecraft "prolific".