Fact is, everyone with a hint of strategic acumen knew it was a nation of 70 million versus a nation of 170 million, the latter having unreachable industrial resources and the advantage of interior lines, a middleweight versus a heavyweight. The former had better win fast, and he didn't.
And the best way for the Germans to have done that was to “Divide and Conquer”, instead, their cruelty to the Russians united everyone against them, even those who despised Stalin.