^^Yeah, that's what I do. Currently, improvement buildings are far too weak. I build almost no factories/labs/markets. I pick about 10% of my planets to be food planets. If I have a good food planet, like a class 12 breadbasket world, that planet can feed almost my entire empire. I spam nothing but farms, Kimberly's refuge, and I'll settle a bunch of farmer citizens on it.
As for my other cities, I'll give them one or some of the starter buildings, like the core mine or space elevator, for example, but beyond that it's mostly cities and morale and colonial hospitals. I do build the major buildings, like financial capital/mfg cap/research cap.
If you have to even question the power of cities you have no idea what you're missing. Focus on growing your population and your economy will dominate everyone else.