The Communist system had little, if anything, to do with defeating the Axis Powers on the Eastern Front. The Germans (and their vassal allies like Romania, Italy, Finland, and Hungary) were defeated by the overwhelming weight of numbers and the massive land-mass of the Soviet Union, not some inherent advantage that the Communist system provided to the Soviets. In fact, the brutality of Communist system was one of the primary reasons why Germany had so much success during the first few months of Barbarossa.
Stalin, being a good Communist, had purged hundreds of thousands of his officers in the months and years leading up to June 1941. As a result, the Soviet Army was practically leaderless when the Germans invaded. While the Soviet troops on the ground, in many cases, fought valiantly in the summer and fall of 1941, entire Soviet field armies (including as many as 700,000 men in the Kiev pocket) were surrounded and obliterated due to incompetent leadership. Germany was stopped short of capturing Moscow in 1941 because, simply put, the German Army was exhausted, not because of the Soviet system. Some German divisions were operating at battalion strength; they had no winter clothes; and they had conquered an area of land in Ukraine, Belarus, the Baltic States, and western Russia that was twice as large as the entirety of France. The Soviets didn't have a superior system than the Germans, they had an endless supply of men, land, and winter to keep throwing at the Germans.
Capitalism, on the other hand, played a crucial role in winning World War II. American Capitalism, through the Lend/Lease Act, quite literally fed the Soviet Union from 1942 to 1945. During World War II, the United States supplied to the USSR the 2020 equivalent of more than $100 billion in food and equipment. The Soviet Army would have had to walk to Berlin, not ride, if not for the 400,000+ trucks and 2,000 locomotives the US provided. The US also supplied the Soviets with some 12,000 aircraft, 13,000 tanks and armored vehicles, nearly 5 million tons of food, and nearly 3 million tons of petroleum products. 60% of all aviation fuel used by the Soviet Air Force during the war was supplied by the United States. Soviet blood was essential in defeating Nazi Germany; but America's industrial base was every bit as important.
Bad Teammate's assessment also completely ignores the War in the Pacific. American Capitalism was the only economic system that could have allowed for the massive logistical effort necessary to transport millions of men and millions of tons of material across the vast Pacific Ocean. By the end of the War, the U.S. Navy had nearly 1,200 capital warships, including 27 fleet carriers, more than 100 escort carriers, and 18 battleships - more than 70% of the entire world's total tonnage of naval vessels. The U.S. military was able to hop from island to island in the Pacific, from Guadalcanal, to Tarawa, to Cape Gloucester, to Saipan, to Guam, to Tinian, to Peleliu, to Iwo Jima, and finally to Okinawa, while simultaneously deploying armies to New Guinea and the Philippines, winning the Battle of Atlantic, and conducting landings in North Africa, Sicily, Italy, Normandy, and Southern France, because our economic system permitted the construction of such a massive navy.
Finally, his assessment ignores that the resource allocations among the United States and the USSR were intentional. The U.S. could have built an Army much larger than 91 divisions (plus 6 Marine divisions), but by design, the U.S. committed millions more men to: 1. Industry on the Home Front; 2. Agriculture on the Home Front; 3. Building a massive Navy to fight a world war on two fronts; and 4. Building a massive strategic bomber force that obliterated Germany's industries and cities. The U.S. could have taken the millions of men in its Navy, Merchant Marine, Army Air Corps, and Industry and put them in front line infantry and armored divisions. But the better resource allocation was to turn America into the Arsenal of Democracy, such that it could supply enough men to keep the pressure on the Germans in the West and defeat the Japanese in the East (and LOL at the hapless Italians), while simultaneously supplying enough raw material, equipment, and supplies to the Soviets to keep them in the War while they were battering the Soviets on the Eastern Front. Google "the 90-Division Gamble" for more.
In short, the political and economic systems of the United States allowed it to fight on numerous fronts across the entire globe: the South Pacific, the Central Pacific, Alaska, the China/Burma Theater, the Philippines, North Africa, Italy, Southern France, Western France, and the Atlantic. The Soviet's political and economic system could never have done that. World War II was not about the triumph of Communism or Socialism, it was about the triumph of American Capitalism.