less than a millisecond for a new npub, less than a second to auth with it, resume spam
paid subscriptions can still be attacked trying to break the security but they can't upload data the server is dropping automatically and ceasing to respond to it
there are many countermeasures, please, you, and quentin, study some network security theory
google and yahoo and protonmail and cloudflare deal with this bullshit every day, and you don't know it until someone finds a crack and jams a wedge in it