You may be conflating metro areas with cities. If you are, it's not a helpful distinction in either case, and not the point I am trying to illustrate.
For example, I could live in Wise County in Texas, and be technically counted towards the population of the Dallas/FW/Arlington Metro, but I would never dream of driving into Dallas from there daily for services, schooling, or work, and if I did, I would be severely disadvantaged, especially if I was poor or lacked resources.
I don't they are conflating metro areas, I think they're describing the accumulation of population a defined area. Metro area can make "cities" seem larger than they are because that population is spread out, but city is misleading as well because it ignores the surrounding population.
Let me put it this way. If you go by city population size, Columbus where I live is larger than San Francisco, Seattle, Boston, Las Vegas, or Atlanta [1]. In fact, Columbus is almost the same size as Atlanta and and Miami combined. Does that seem right to you?
If I were you, for your argument I would use population densities.
But you can’t bucket a million people living in thousands of square miles as the same as a million locked together in a suburban sprawl connected with rail and roads. Look at London. Take away the boroughs and what is really left?
