I agree with you. I just don't think this particular instance is representative of an actual attack. Whatever we code for it can be circumvented by a smarter player. Not that we shouldn't code it, but let's be mindful of what we are solving for. 

Real bots with WoT (because people will gladly sell their nsec to a bot maker and restart their accounts) will be much more demanding than this simple attack. They are going to look, act and work as a real human. 

Every message in Nostr with immediately get 200 replies with products and opinions from people that are paying for it by nsecs of previous real users with WoT and so on. Any serious defense on this will need to include a complete understanding of the entire network or it will be something selected by the user, like just people that I follow.