Hitler probably also thought that as unpopular as Stalin had to be with his soldiers, it was easier to convince them to surrender...but if suddenly Stalin were replaced by a more popular figure, then the Russians would be more determined to fight against the Germans. So Hitler actually preferred to keep Stalin in power, which in hindsight, was a big mistake.
IMHO the allies best general was none other than Adolf Hitler. This is not to diminish our sacrifices or our skill. But all of Hitler's defeats before 1943 were avoidable, and many of his victories were not exploited.