Gotta say that I have been reading on the history of Southeast Asia in the recent weeks, and in this particular region civ switching and insistence on lack of persistent cultures and identities across history feels unconvicing as hell to me... Premodern Vietnamese, Khmer, Chams, Burmese, Mon, Malays or Tai peoples (okay, as a whole in this case) sure as hell seem to have had pretty damn long continuity of cultural practices and some sense of "their" people and land, and distinction from other groups, and claims of legacy of older dynasties. The more I read of the academic history of the region the LESS positive I am about civ switching in terms of historicity, whereas I suppose it "should" be the opposite. Sure it was not modern 20th century nationalism but there is something deeply suspicipus for me in this anti essentialist revisionism going all the way into the opposite direction (as oft happens with revisionisms).
18th century Burmese and Vietnamese had strong enough identities to frame their kingdoms as those "of Burmese/Vietnamese race", invoking glory of past centuries and writing chronicles "of Burmese/Vietnamese race" and consciously embarking on campaigns of cultural assimilation (or basically ethnic cleansing) of Mon or Cham or Khmer or whoever, and both of them fought wars against Siam who totally were mass mobilized in the name of "Tai race". All this sure as hell won't make it any easier for me to feel emotional connection and an intuitive narrative with Khmer casually becoming Vietnamese and then Siamese.
By the way, there is a massive degree of archeological continuity between neolithic Cambodia, bronze age Cambodia, Funan, Chenla and Angkor; and of anthropological continuity of customs of post-Angkor Khmer people between 16th century and modern era. So why exactly can't I play as Khmer from ancient to the modern era, if it's pretty much their history IRL? Sure, not every culture has such long continuity, but also not every culture has a melting pot nature of say English.