It's actually pretty important, because the crux of your argument is that they're moving to places with much a lower CoL. If people are moving from NYC to LA/Seattle/etc., your argument doesn't really hold much water.
> or you could take my point that there is a reason why people are moving out of places like NYC in favor of less dense cities that don't smell like urine.
Where are you getting that information from? As far as I can tell, NYC has had about a 6% population growth since 2010. It actually matches the US overall population growth pretty well, which is pretty impressive for what is far and away the most populated city in the country.