It's absolutely true that the Holocaust hit several groups with the same brutality as the Jews (Slavs, Romani, Gays, etc.). However when the Holocaust is taught about, it's usually with a strong focus on Jews and antisemitism. Additionally, Russia has been built up as an adversary throughout the past 50-70 years. With that in mind, I don't see it as strange that the "Holocaust guilt" is centred around Jews, and that Germany finds it easier to oppose Russia than Isreal.