While ethnicity and low culture aren’t everything, they aren’t nothing either. I think it should be held in balance with linguistic and political history. I would argue Civ 6 made a conscious choice to locate more of a civ’s identity with low culture, and thus “the common people” in its decision to use folk music for the soundtracks, where possible. Older games mostly used patriotic or “high culture” music.
France is an excellent example, because their ruling class, the borders, warrior nobility, and the name were/are Frankish (Germanic). Their language, administration, and religion were inherited from the Romans (Italic), and the common folk are mostly the original Gallic people (Celtic). French identity is a mixture of those three influences into something new. Focusing too much on the ethnic continuity of Gaul and France risks being genetic essentialism. However, focusing too much on the Germanic and “high culture” aspects of France reproduces old, uncritical Great Man historiography. Neither gives the full picture.
Just an aside here, but just to note that intellectually, France identifies far more with Rome than Gaul. As in, regional museums in France (at least, 30 years ago when I was last there) which have artifacts from the Classical Era, identify even obvious Gallic material as 'Roman' if there is any connection, no matter how tenuous, with the Roman province of Gaul or the Roman Empire in general.
And in the somewhat related debate, which at times has gotten even more rancorous than some of the posting here, over the 'ethnicity' of the 'Barbarians' who overran the western Empire, virtually the only point of agreement among the various scholars after spilling reams of ink over it has been the conclusion that ethnicity in the Gothic, Frankish, Vandalic, Lombardic context had little or nothing to do with genetics or race at all: they were all tribal confederations of various kinds, and the similarities that held them together were cultural and political, with many of the cultural attributes linked to status - that is, a vertical structure rather than a horizontal. As posted above, the 'common people' in Post-Roman Gaul remained Celtic/Gallic, while the higher-ups adopted Frankish cultural and political norms. But the overall genetic features of the population did not change that much (cue the discovery from DNA studies that despite all the admixture of Angles, Saxons, Scandinavians, Normans, etc the same genetic group has been living in the Cheshire region of England for 7000 years or more: genetics of groups apparently does not change easily). Culture, and especially physical attributes of culture (costume, architecture, weaponry, jewelry and decoration) change constantly, and frequently from mere contact rather than 'conquest' or migration/invasion.
Point to all this discussion here is that the genetic makeup of a population or individual is less important that the cultural identity self-selected by that group or individual: so Catherine was Russian, Nader Shah was Persian, and despite having German genetics going back as far as we've been able to trace and living in Germany for 11+ years, I'm still American - whatever that means.
And the final point to the Civ game is that in a game that attempts to cover 6000 years and the world or cultural/political groups the only workable system is to use the widest possible definition of culture and group to include all the myriad possibilities of genetic, cultural, political mixes that have occurred, and to admit that the exact genetics and culture are utterly Unimportant in the game unless they manifest in obviously different social, civic, military, political religious attributes that can be modeled in-game. The fact that in a population one group spoke Gallic Latin and another Germanic Frankish or a leader spoke German from birth in a country that spoke Russian means nothing except in the voice-acted Leader graphic, which is, frankly, immaterial to actual play of the game.
