"Nationalist extremism" in Ukraine is mostly a myth created by Russian propaganda (you can find "nationalist extremism" in almost any country), as is the division between "Ukrainian-speaking West" and "Russian-speaking East". The language situation in Ukraine is much more complex than that. Even in many regions east of Dnieper there is a significant, if not dominant, percentage of Ukrainian-speakers. Besides, in some regions one can observe the difference between predominantly Russian-speaking cities and predominantly Ukrainian-speaking countryside. This is one of the problems the Russians encountered in Kherson region which they had occupied during this phase of the war. They had expected (based on their propaganda) it to be mostly Russian-speaking and pro-Russian, which turned out to be completely wrong (it's even more so in case of the northern Chernihiv and Sumy regions where they have now withdrawn from - despite bordering on Russia, they are still predominantly Ukrainian-speaking).

There's also one serious problem with that clash of civilizations map. Ukraine has even more reasons to align itself with the West than Bulgaria, Greece and Romania since a significant percentage of Ukrainians are not Orthodox Christians. Yes, statistically Ukraine is a predominantly Orthodox country, but statistics is a tricky thing. I'm from Western Ukraine, and Orthodox culture is rather alien to me. I'm not religious myself, but most of my ancestors for the last four centuries were Greek Catholics (as well as some Roman Catholic non-Ukrainians). Yes, they must have been Orthodox Christians before 1596, but that was long ago; Western influences are now felt much more. Even though Ukrainian Greek Catholic Church follows the Eastern (Byzantine) Rite, it recognizes the Pope and has a lot in common with the Roman Catholic Church, especially from the point of view of the average believer (and had even more in the past when it was using Latin), which is why Greek Catholic Ukrainians in Poland and other countries have no problem with going to Roman Catholic churches (and they will definitely not look for an Orthodox church).

That said, Orthodox culture does have a lot of influence in Ukraine, and Ukraine still has a long way to go to become truly aligned with the West, and I really hope this war becomes the catalyst.