The Soviet Union won the war despite Stalin too. 3 years before the war he purged his entire officer corps. When the war came there was nobody with any real experience. For the first 2 weeks of Barbarossa, the Nazi invasion of the USSR, Stalin couldn’t make a decision to save his (or his countries) ass. Stalin was good at throwing “flesh waves” at the Germans, giving every third man a rifle and telling the ones without to grab a rifle off a dead soldier when he fell. You want strategy? Look to people like Marshal Zhukov. Incidentally, Stalin hated Zhukov because he was as popular as Stalin himself. It was only that fame that kept Stalin from killing him.
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And then there was Leningrad, a city Stalin always hated. He would have let the Nazis destroy the city if he could.
After the war, he had many of the heroes of Leningrad executed.
And I still believe Stalin let Hitler have his way in the areas of the Soviet Union where the Jews primarily lived, knowing that Hitler would take care of Stalin’s “Jewish Problem.”
And Marshal Zhukov won his initial fame in the Soviet Far East against the Japanese in the Battle of Khalkhin Gol, where his innovative use of tactics beat back the Japanese. Those same tactics in an upgraded form proved vital in beating back the Germans from 1943 on, and Stalin—despite his disdain for Zhukov—had to rely on this General right to the end of World War II.