re: There were early signs....
I won't deny he's recycling concepts. I would have to think about how many times the "invisible demon from beyond" has been used, ("Hat Full of Sky," "Wintersmith," and "Thud" come to mind).
Still, I would give my right arm to write with as much wit and skill as he does. I suspect that if he ends up in a rest home with a drool bucket, he'll still be a better writer than many others.
Sure as hell he'd be better than me. I consider it a good day writing if I can get one clever concept or a witty use of words into five pages. Pratchett fires off about six of those per page, many of them fairly profound.