I think that you are most likely correct that there are a large number of "public squares" and that people sometimes over state the importance of a given one.

I think that you are most likely correct that there are a large number of "public squares" and that people sometimes over state the importance of a given one. However, I still think it's likely that among those public squares, certain ones are more important than others. If I had to guess I would say that Hollywood, network news, and social media are the biggest players. I suppose someone could probably do a study to try to determine which platforms are most important. For example, they could track where political slogans that eventually go mainstream originated.