No idea on technical stuff. I know with certainty that hex is worse from a user facing perspective. A bunch of seemingly random characters. Whereas npub is clearly associated with nostr.
in this case it already has the "nostr" part logically separated the evolution of the web was from the hyperlink, to typed links solid does typed links which is the most advanced form of the web, npub was a hack because nostr doesnt have typed links (yet)