Compare figure 3 here in the #atproto / #bluesky paper
https://bsky.social/about/bluesky-and-the-at-protocol-usable-decentralized-social-media-martin-kleppmann.pdf
To the diagram here:
https://bsky.social/about/blog/5-5-2023-federation-architecture

The paper figure is a lot cuter, but by linearizing it and presenting it as two parallel tracks they have obscured the most salient feature of the network: the big relay in the middle. Beyond "centralization bad," that pins down most of the undesirable and dangerous features of the protocol, and makes it seem like theres a lot more choice than there is.

Since the design purposefully hides the architecture: you dont know where your feed generators are drawing from, or those used by your friends. So you cant know what the effect of choosing a different relay would be, aka the main relay is always indispensable. Importantly the relays subscribe to you, you dont push to the relay, and since you arent really supposed to operate your own data store, you can be dropped from the network without knowing - the relay serves as an unaccountable point of moderation.