As it happens nostr was based on Scuttlebut, but lots was removed.  IMHO the design was not great, but just about works, and the simplicity gained developer interest (build something in a weekend).  It's more complex now.

I'll have to look a bit more at SSB and per user chains to fully understand what you mean, but you may be onto something there.  Thanks for the pointer.

There's plenty of possible caching strategies.  Nostr doesnt really have one.  My understanding is that primal were working on something.  It would be good to see what.  First thing to establish is that there is work to be done, and I hope you've helped to do that.