I think you're missing the point that many of those moving out of the really big cities are going to the same smaller cities. Taking Austin as an example, it's

I think you're missing the point that many of those moving out of the really big cities are going to the same smaller cities. Taking Austin as an example, it's growing by leaps and bounds. The gentrification is indeed happening. If the outflow from the really big cities was equally distributed (say, as percentage of city's population), then your view would be accurate. But that's not what's happening.