Ethnic Russians were the largest proportion of the killed in action by quite a margin, let’s not pretend that they weren’t doing their part. Ukraine was too, of course - the people that pretend Ukraine just jumped ship and shacked up with the Nazis at the first opportunity are doing an unbelievable disservice to the millions of Ukrainians that died fighting the Nazis - but the huge population disparity between Russia and every other Soviet republic does show in the data.