What has shifted is the borders of the ruling empires but a distinct Ukrainian population has remained throughout. The fact that they did not have the military power to resist the two empires that ruled over them does not negate that as a nation they existed. Ask a Ukrainian today if he is a Russian; he has a clear and distinct identity. No amount of historical rule by either the Poles or the Russians can erase that. The Ukrainians are not Russians; live with it!
Irish was the main language spoken in Ireland up through the late 1800s, and likely would be today but for the troubled history of the island (aka British rule). Irish has nothing in common with English. Comparing that to the relatively similar Ukrainian and Russian languages is silly.