I saw the news that ATProto relay is now very cheap to run, and went to check it. Turns out "cheap" means 10 GB RAM, 500 GB SSD, 50mbps bandwidth. This is more than minimum Ethereum node requirements, and I am not sure how it could possibly be worse than that.
Needless to say, relay is only one component in their laughably inefficient system, which is still not decentralized in any meaningful way.