The main problem that I see is that ActivityPub doesn't address the problems with federated socnets which were already known about before it arrived. Being able to migrate accounts from one server to another, having a nomadic identity which is resistant to server outages and also being able to have privacy controls over who sees what. All of those things mean having a key based identity rather than a domain based one.
The war reference relates to the early development of Mastodon. At that time it looked like Mastodon was just going to be another identi.ca or Twitter clone - a single server system with many users. There were numerous federation bugs and seemingly not much interest in fixing them. Fortunately those fears turned out to be unfounded. As Mastodon got more popular more instances appeared, and the earlier attitude that other instances were traitors to the One True Instance went away.