It's not a perfect model, but it's decently close. If Lemmy had a way to distribute server ownership to a group of individuals, that would be even closer.

If I was a whiz at developing, I would love to build that kind of feature.

I understand your concern of external threats to an anarchistic society, but I would just remind you that plenty of centralized governments/societies have also been conquered by other centralized powers. Being centralized by no means protects you from that threat. I think the more relevant factor is just overall size of the opposing force.

It doesn't matter how weak hamsters are compared to you. If enough of them attack you endlessly, eventually you will succumb, if for no other reason than pure exhaustion lol.

However, there are clear examples IRL of far smaller and weaker decentralized forces successfully resisting a much more powerful centralized force. The VietCong vs the USA in Vietnam, the Mujahideen vs the USSR in Afghanistan, the American Revolutionary forces vs England, the French Resistance vs the Nazis, etc.

I would highly recommend the YouTuber, Anark. He has fantastic content discussing all aspects of anarchism, including defense. He also has links to many other great resources to learn about Anarchism.