"So "the Heavens" persist, and all the Netherworld bureaucracy persists (or has established itself over time?), but everything else is kind of static because the powerful being who can actually affect the cosmology are all gone? And that's why things are unfair in the way they are -- because there's no one tinkering with them?"

I guess if someone tinkered with things they could theoretically get even worse, lol, but yes, this is a fantastic observation! The gods made the world this way and now they're all gone and the world just is this way, for better or for worse.