Dear Richmond,
Here is Eruvin 101. Even if a city contains a reshus harrabim deoraisa there are simple methods to build a proper eruv between houses. There is extremely complex methods to build an eruv around large parts of the city as well. The fact that there are kosher eruvin in Brooklyn, doesn’t mean that there is no rh”r. Maybe I completely misread your posts. But it seems like you are arguing on this fact.