In fact, specialized and diverse cities are actually complementary, serving different roles in a market economy.
Many firms start their lives in a diverse city and eventually relocate to a specialized city.
Diverse cities foster new ideas and experimentation they serve as laboratories for innovative firms.
Once a firm settles on a product design and production process, production is likely to be more efficient in specialized city that fully exploits localization economies.
In other words, diverse cities foster innovation, while specialized cities foster innovation, while specialized cities facilitate efficient production.