You're correct that increasing resolution to the county level can inflate the size of states with more counties. This kind of map wouldn't be appropriate for a state by state comparison at all; instead, it's more useful for a county by county comparison. It's just a different resolution of administrative boundary and there are limits to that.
A lot of U.S. data is reported at the county level and comparing across regions within or across states without worrying about the geography or shapes of different counties can sometimes be helpful. Adding population as a size dimension and filtering to a single state can also help mitigate the distortions.
A lot of U.S. data is reported at the county level and comparing across regions within or across states without worrying about the geography or shapes of different counties can sometimes be helpful. Adding population as a size dimension and filtering to a single state can also help mitigate the distortions.