Why aren't Russians seen as a protected victim class even though they suffered more than almost any other group in the 20th century, including the death of 27 million of them at the hands of Nazis?
In large part because the Nazis killed plenty of other groups in Eastern Europe as well, many of which were much more expressly and definitionally targeted than Russians were. Also, most people
do (rightly) see Russians as victims in the specific context of World War II. The fact that they fought back and eventually, thank God, won, militates against their being treated as the Little Nell of world powers, though.
Why, despite this history, are their concerns about Nazism in Ukraine not taken seriously?
Why a country with this history would be so flippant and unserious about it on the diplomatic stage is an excellent question, yes.
I can think of a certain other country that is allowed to get away with horrendous war crimes and use "we were victims of the Nazis" as an excuse.
And do you think that that's a morally acceptable state of affairs, or not?
Even though Palestinians are completely innocent of collaborating with Nazis,
[
dubious – discuss]
while Ukrainian nationalists aren't.
Depends on which Ukrainian nationalists. There are definitely people in the Kyiv and Lviv local governments whose preferred historiographies trend in unsettling directions, but internal ideological spectra have a way of temporarily ceasing to matter during wars of national survival.