I don't think you can say "this is complete nonsense" and "this has since been fixed" in the same comment. Also: don't use ECC signatures as MACs. Signatures are not MACs.
Could you explain more? What are the downsides of a signature vs. a MAC here?
This makes sense in nostr, because anyone at any point can mint new public key and start posting events and other people are free to start following them, from which point they can ensure that the new events are coming from the person holding the same private key. And this is what relays and clients do.