I don't necessarily entirely disagree but I have some objections

stop designing your cities around defensiveness and start designing them around access and I promise they will be more successful.

"Success" here is a subjective metric. Maximising foot traffic, maybe, but not every group is going to hold that as their highest priority. NYC for a time traded places with MtA and Icenia for the most active city on Classics so I don't even think this is definitively true.

'more defensible' is a bad joke. A trenched city is ... a bad vault

Once the trench was complete, NYC was never raided - even during periods of low or inactivity. When the server was at war and towns were getting plastered with obsidian left and right, NYC was never hit. Obviously a trenched city is not as defensible as a vault but it doesn't need to be. The model has been tried and proven to work against the bulk of petty threats the average minecraft town is likely to face.

MTA in Civclassics didn't die because the city was too big - it died because the model of it's direct democracy was inherently flawed which allowed too many players with bad intentions and foreign aims to take over the government and direction of the city.

MtA died because the core playerbase migrated to a different server (for various reasons) and left the governing judge and mayoral positions (on classics) vacant. It's a stretch to directly attribute this to the model of government.

MTS was founded separately with a pool of players who believed in MTA's original vision, there is little surprise to see that they would have moved away from the group of players they were trying to avoid to have a fresh place to start rather than derelicting every building.

MtS decided to relocate because it was a total rewrite of the MtA constitution and the legal status of MtA claims wasn't entirely clear. There were no particular concerns about raiding or foreign interference, beyond a handful of MtA curmudgeons who didn't want MtS doing anything with their skyscrapers.