That’s only partially the case, at best. The Uniate church was much bigger in Ukraine before it fell under Russian domination, and the whole area was much more religiously diverse. What is it you think the similarities in language means? Almost all European languages come from one proto-language, which branched off into various forms, that has nothing to do with questions of national identity. Spain is not Italy, is not France, England is not Holland or Germany, Russia is not the Czech Republic. It’s a meaningless metric.
My point was that they are/were closely related to each other, suggesting that they come from similar cultural and ethnic roots. It's not a meaningless metric.
As for the Uniate church, it seemed Poland sabotaged that more than the Russians ever could have.
Ruthenian Uniate Church - Wikipedia
en.wikipedia.org
Poles regarded Ruthenians as a conquered people. As such, Ruthenians became a second class people in society, their culture backward compared to the other ethnic groups in the Commonwealth. This delayed the church in recovering from the predations of the Reformation. While the Ruthenian nobility had equal rights with the Polish nobility, by the fifteenth century their ranks had been thinned by war and waves of emigration to the east. The Poles who took their place came to control the sejm. If the Ruthenian aristocracy wanted to profit from its equality, it had to become Catholic and Polish. Intermarriage played a great role in the assimilation of the Ruthenian aristocracy; usually the Catholic faith prevailed. As a result, few Orthodox aristocratic families were left in Galicia or Podilia.[8] By the second half of the sixteenth century, Ruthenian nobility had little reason to feel discriminated against. They had kept their wealth, had access to the highest offices, and were socially accepted as equals with the Catholic nobility. By absorbing the Polish form of Western culture, they were also the first to be lost for the Ruthenian people. With the loss of the elite, the Ruthenian Church and people increasingly lost leadership, representation in the government, and benefactors for church-sponsored programmes.