Calling France an ethnic state is saying the Normans are the same group as the Provençal. It's like doing the same in Spain; a sure way to lose new friends. France and Spain are also old empires.
Japan is something else. The description makes sense there. Maybe also for the Nordic countries of Europe.
At the level of spoken language, Han natively speak several mutually unintelligible languages; even at the written level, most of the mutually intelligibility only exists in the more formal registers. Are Han really one ethnic group then? Or more like a family of closely related ethnic groups?
> Japan is something else. The description makes sense there
Are Ryukyuans the same ethnic group as Yamato Japanese?