You are tying yourself in knots trying to retcon this war. Russia was able to use heavy-handed tactics during WWII but can't now because Ukraine is too big and has too many resources but Nazi Germany didn't? Russia was engaged in an "existential struggle" during WWII and is similarly engaged in one today, but somehow that justifies going lightly now.

Come on.

A much simpler explanation is available, and one that doesn't require so many internal contradictions. Unfortunately, it does not lead to comforting conclusions.