Even before the arrival of #atproto was the question of what #decentralization of the web means quite murky, with multiple competing protocols at different abstraction layers. As frequently said, at one level the web is already decentralized so envisaging pure #p2p is also conceivable, why the need for #activitypub (or whatever) "servers"?
We come to realize that the problem is not well defined. First of all it does matter what you assume about the distribution of silicon and networks...
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