As I'm sure you know, the relation between article quality and site quality is complicated.

HN's approach is to focus on the quality of the article, because that's what maximizes interestingness for the reader. We penalize sites that mostly produce bad articles, but we override that penalty for the occasional good one, which this is. I'm happy to change the URL if there's a better one but I don't think it makes sense for HN readers not to see Brennan's remarkable piece.