A better question is to ask yourself what nostr solves.

Nostr sends notes, and other stuff, from one user to another, using relays (web servers) in realtime.

This is better than the status quo, because if one relay goes down, you can use another, and you (hopefully) have not lost everything.

#pubky is provably censorship-resistant DNS.  It has millions of nodes, and 15 years of track record, most famously via Bittorrent mainline.

Censorship resistant  DNS is a big idea because it allows anyone to express themselves.  To stop it you would have to take down 20 million nodes (as opposed to 2-3 relays) and then 100s more would spring up.

Each project does different things.  Nostr improves on the status quo by relaying notes.  Let nostr be nostr.  

#pubky solves a big idea which is to decentralize DNS, which has become the acchiles heel of the web.  It also gives access to dozens of massive nettworks (e.g. git) many bigger than nostr already.

Since they both use the same private key users can have one or both if they choose.  There is a powerful intersection that some of us are now exploring.  My mind is blown with the possibilities.