Your question is based on a false premise.

The Russo-Japanese War and World War I didn't involve the Soviet Union (they involved the Russian Empire, which was a very different beast from the USSR); Poland didn't take part in World War I (I think you're thinking of the Polish–Soviet War, a separate war and took place during the Russian Civil War); the Soviets WON the war against Finland; and the Soviets didn't defeat Nazj Germany because of the winter. At most, it can be said that the winter caused the failure of Operation Barbarossa, but that's not remotely the same thing as helping them successfully take Berlin.

That being said, much of the perception of Westerners during the Cold War of the perceived invincibility of the USSR was incorrect, but that had little to do with their military power and everything to do with their economy. Collectivization during the 1930s basically destroyed Soviet agriculture and premiers after Stalin were forced to buy grain from abroad to prevent starvation. These problems were later compounded by the high price tag of the Soviet War in Afghanistan and the cleanup after the Chernobyl disaster coupled with revolts by the Baltic states.