In the FAQ at the bottom of the post, the author mentions that this proposal is just the AT protocol (BlueSky) without the active, "firehose" component.

I don't think this is a real proposal, but more a thought experiment about how a static site could integrate into BlueSky. I saw a few similar efforts to integrate the "passive" components of ActivityPub into static site generators so that you could make your static blog consumable via the Fediverse.

In reality, if you really wanted to publish your static site blog posts on BlueSky, this is probably a good place to start! As you mention, there are some serious usability issues with doing everything by hand, but you may find that acceptable or invest in workarounds. Maybe it's possible to use your BlueSky identity so that you aren't in the business of managing keys. Or maybe you could use a script or static site generator plugin to pull credentials from somewhere.