I think immigration to shift around ethnic minorities can absolutely be relevant. Especially with relatively small countries where few people already makes a large difference, if, usually, their direct neighbours are having a conflict that makes lots and lots of people migrate there.
For instance, Jordan has a population of about 10M, but about 2M are Palestinian, and for a while they had about 1M Iraqis (most of them have returned, leaving behind about 130k)
And more recently, 1.4M Syrians fled there.
At least according to https://en.wikipedia.org/wiki/Jordan#Immigrants_and_refugees
That’s a far cry from the 90-100% the game likes to claim are ethnic minorities in any given country, but it really is a significant number that is going to have large repercussions for this nation.
Most countries are simply not facing that kind of extreme, largely local-instability-driven influx though. So perhaps this would be better adjusted through a special variable in the future. For most places, the differences over time are gonna probably be in the 0.1 - 1% range, perhaps. (This is a complete guess, mind. I have not checked any stats what so ever to arrive at that number and am happy to be proven wrong)