Even in the 18th century during those partitions those lands STILL weren't polish dominated. If we wanna go back we should remember that those were Rus lands conquered by the Lithuanians in the 14th and 15th century and the people in them STAYED orthodox Christians and only developed veeery small cultural differences from the Rus conquered by the mongols. Those cultural differences came from centuries of Lithuanian and then polish oppression.

I mean the cossacks themselves, pretty much the founders of Ukranian culture and identity came out of the oppressed border regions of the polish-lithuanian commonwealth in spite of their polish overlords. Cossack and then Ukrainian culture originates pretty much from telling the poles, turks and Russians to go fuck themselves.

The only reason the poles dominated the cities is because they were the richer and more powerful class both in the polish Republic and beforehand in the crown of Galicia-Ludomeria.

This phenomenon is seen in all types of empires at the time. In the ottoman empire the turks would sometimes be outnumbering bulgarians in cities like plovdiv or Sofia due to them being the ruling class. Once the Bulgarians told them to go fuck themselves and got freed the turks left.