In today's Let's Play... not a single city as large as 18 on Turn 233 . And yes, you're of course right that we probably won't need an encampment in every city. But your largest cities? That have already been your unit producers all came and have specialist buildings, and walls so that the Encampment gets a ranged shot? I don't think too many people are going to build over encampment districts, nor forego them for defensive fort purposes and specialization purposes unless it's a city deep in the back of an empire.