Hi
I love the change, from city-states to trans-regioanl ethnicities. Which is what a couple of the comments, were trying to describe, Dorians and Ionians for example have different origins, Dorians supposedly come from Doris and some question over if they were marauding barbarains initially. While the Ionians were descended from Ion. They became nemesises when the Dorians invaded the Peloponnese and caused the Ionians to flee. Supposedly from Euripedes and the refugees created Athens. The differences between each etjnicity are quite apparent, Even in the time of the Peloponnesian war, Many held the ionians to be weak and effeminate, while believing in the great military prowess of Sparta and the Dorians, in which Sparta led the ethnic Hegemony. Sparta's military prowess is very questionable at this stage, and lives mostly of on its history rather than present. but that is a different debate.
However history is too complcated and lacking in sources to clearly say that it was Dorian v Ionian and there were many interests at stack. (not as black and white as it appears)
I am doing my dissertation on Greek ethnicity at the time of the Pelo War and it brings awareness of a commonly ignored trait of Greek warfare and diplomacy.
However, historical this does struggle as you would in theory have to change Syracuse, Corinth,
Doris, Crete although it is good you singled them out as they were like the Achaens mainly mercs, and mainly brought by Athenians.
Therefore the solution is to create a mod that joins all the dorians up and all the ionians up etc.
Although places like Rhodes and Camarian, Naxos , Corcyra would have to be incorporated into the ionians for accuracy.Also what would you call Argos big enough to be their own faction in the game, hated Sparta but deeply Dorian. Instead the ethnicity idea works better as a diplomatic mechanic, which I think it is in the orignal game. Could be improved however.

Thanks I hope it answers many of the comments, and for allowing me to write this.
I am also happy to answer any questions .
Thanks, once again
George