It's a bit precious to point to the Greek borders and say "look, there's Greece" when you're pointing to a territory in which a half million people were forcibly expelled based on ethnonationalist politics and ideology, only 100 years ago.

Likewise to "French ethnicity", a place where government policy is still actively engaged in destroying minority languages (and their cultures) and has been since Napoleon.

These "ethnic" borders you're pointing to are as much a product of political maneuverings using ethnicity as a platform, as they are any kind of "natural" product of ethnicity.