Being fairly introverted, I don't know. I can say that living in the sticks has been at least as social as living in the burbs. But folks out here get along better. By that, I mean on my road, I have hung out around a fire with several neighbors. The back to the land hippies, the full on commune hippies, the independent contractor, the religious nutcase, the heavy equipment operator/conspiracy theorist, the retired real estate agent. We all get along, sometimes more, sometimes less, but in the sticks, you get to know your neighbors. In the burbs, you may know your nieghbors, or not. But the overabundance of people means you select for the ones who are similar, until everyone lives in a bubble of similar people.Which places foster loneliness more? Social isolation.
Population pressure forces people to choose people to befriend, and ignore the rest. I think this, more than anything leads to the political radicalism that seems to be a theme across the last decade. People virtually and physically separating themselves from differing opinions. And the nasty shock that goes along with finding out that not everyone agrees with everything I believe. In the sticks, this disagreement is obvious, and easily overcome. In the burbs, not so much.
I have never lived in the city as an adult, so I can't compare. But since nothing else seems to work there, I can't see why this would be different.