The Soviets did do by far the majority of the fighting. And dying. Of course that was also a symptom of the brutal and inhuman regime: soldiers were sent into battle in suicidal human wave attacks, sometimes even without a weapon, because Stalin didn't care about their lives.
But they were fighting the brunt of the German military machine, and they did defeat them. It wasn't North Africa or Normandy that broke the Nazis, it was Russia.