This stream lacks any blog posts that haven't been specifically published to atproto. Conversely, I see RSS feeds for the content in the stream, like https://bsky.app/profile/did:plc:byf7jvh3yvhffackiumpddtf/rs... (if RSS feeds exists for every profiles then I'd argue that atproto is a strict subset of RSS, but I'm not certain how that feature works). The stream may give you every blog post that was published to atproto, but that's already a small subset of long-form content on the web.
> Notably this is not possible with RSS,
The web supports blog discovery so well that people forget it exists. A simple Google search can find a very large amount of content, much available over RSS/Atom. Many web-based feed readers index the subscriptions across all their users to help with discovery. Here's the Feedland firehose, for example: https://feedland.com/?everything=true
I don't think its helpful to argue how complete the Google index is vs a bluesky firehose though. Most users are drowning in content and discovery is about search and filtering. There's lots of interest right now in vouching for the content of others: https://susam.net/wander/wander.js, https://codeberg.org/robida/human.json, https://www.manton.org/2024/03/11/recommendations-and-blogro..., etc.