[…] they’re always using the same credentials no matter the website they use and no matter the website they can interact with everything that ever happened on the servers, no one has the power to prevent users from seeing some of the transactions that happened (no admins) because the website they use are just a front used to simplify interaction with the servers. […]

Hm, IIUC, this is one of Bluesky's issues that the linked blog post was pointing out — if joining the network requires one to mirror all existing data, it makes it prohibitively expensive for anyone to spin up a server to join the network if the size of the network is enormous.