If you design a city, and then design a slightly better or worse city, and repeat that process until every new modification only creates a worse city, is that not at least a locally ideal city evolved through design?

There is no such thing as an ideal city. Everyone who lives in it would have different needs, and these needs change over time. City dynamics are unpredictable. How can you design for an audience that is at once unpredictable, and does not know what it wants?