From the article …

This effectively means that, if you get banned by the Bluesky company, you’re out. Sure, you could still host your own Personal Data Server, wait for a non-existent independent Relay to fetch your data and interact with users of third-party Bluesky applications. But you won’t: you’re effectively at the mercy of the Bluesky company.

Point two, and more importantly: this approach provides an “exit strategy” in the event that Bluesky “goes evil”. Right now, that’s false: parts of the social network are still centralized and it’s impossible to avoid that. But even if we limit ourselves to PDSs and Relay, the current situation is that federation is only achievable in theory and no one has done it in practice yet.