Well, the complaints about the starting castle are more about the army. Because you need to defeat guards with 6000 hit points, and a single starting spawn point is usually not enough for a decent build-up. In Might and Magic VI, there's no such requirement; the guards in neighboring zones have 3000 hit points, and you can gather some money and resources from three zones. Also, you can build a Watchtower even with the starting money, which significantly increases the army's offensive power. I would say that the Swamp is one of the most resilient castles. And regarding ranged units, it's the most resilient overall.