In any practical sense the Soviet Union did in fact do the lion's share of beating the Nazis. They opened an extra front and sent in a staggering amount of troops. I don't see why it is still so demonized, except when you view it directly through the lens of US propaganda.

Their death toll, such as it is, is not even a tenth of the incredible casualty rate of the British. It does not need to be said that they're nowhere near as demonised, except in India. The scope and depth of a civilisation's deaths is not actually all that relevant to how much people hate it.