My contention is that median variability of cultural attributes between those cities is signifcantly less than median variability of cultural attributes in US cities.

That is a fair observation. To clarify, you think that makes it harder to find political solutions because people don't feel they are "in it together"?

Exactly. The easier it is to find differences in your group and another group under the same organization, especially with a weak overarching culture, the less likely those groups will coordinate politically and economically.