I don't understand your version of centralization. If my mobile could talk to your mobile directly, that would be basically full decentralization. If my mobile talks to my server which talks to your server which talks to your mobile, that's more decentralized than most servers also having to go through one of a few relays. that's my understanding of AP vs AT protocol.
Re interfaces and instances, fedi gives developers more options than BS does because, see above.
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