Hmm this sounds less good. The problem I was anticipating with making city defense strong is that the AI only takes settlements by luck, when they once in an eon use siege weapons and melee units. In vanilla I typically have the impression that after the first wave is blunted, the AI doesn't mount a sensible attack anymore because it doesn't create formations and instead sends their units uselessly to their death. This means that the player, who can work with the system, has another disproportional advantage. Artillery is really good, maybe this is a pointer to a better system: Give all siege units 3 range but make them weak against field units while strong against cities (I think you already have this except for range). That way you need a lot of them to make a dent in a field army (instead of owning them as you do now) but a couple as support for taking cities is fine.