At the levels of density seen in Paris, San Diego could house 16 million people. That's city proper. The metro area could house 226 million people.
You're gonna have to do a lot better job convincing me that 16 million people would move to San Diego if they just built more housing. Let alone 226 million.
Yet the rent in Paris is still too high for an average French resident; and while rent is lower than in San Diego, the price of an apartment is higher. And, of course, median salary in San Diego is far higher than in Paris.
Twist do you think happens to every city that has reached 16 million people? Did they become more popular or less? Given that I’ve lived in a city of that size, my answer will differ from yours (they become more expensive, not less).
I’m confused on why you think paris is affordable and San Diego metro could somehow have enough water to grow to 220 million. The nearest comparison I can think of is south China Bay Area population (87 million), and if you think that those cities are affordable…I’m guessing we really have to agree to disagree.