I recently watched a video on youtube from a history teacher who made this exact claim. He is a self described communist so I take everything he says with a huge grain of salt. As a German I know a bit about WW2 history so I immediately understood where he was coming from, but also that he was heavily manipulating the audience. He of course did NOT mention Lend-Lease and the enormous amount of food and military aid received by the Soviet Union during WW2. As I understand it there was also controlled leakage of intelligence to the Soviet particularly when it comes to enigma. I've heard all sorts of arguments about what won WW2, for instance I remember seeing a documentary as a child that argue that Britain's superior radar technology had won the war. So here is my question: would it be fair to say that without cooperation of the allies the USSR wouldn't have won? At least not in time, because by the end of 1945 America would have been able to drop a nuke on Germany, and end the war.
This answer from u/Georgy_K_Zhukov goes into a lot of detail about industrial capacity and overall "warmaking potential" of not just the US, but of the other major powers involved in the war.
The notion that the US didn't contribute anything to WWII is classic second-opinion bias -- we get told that the USA is back to back World War champs, and then learn later that the US entered WWI very late and WWII only after France had been defeated and Hitler had invaded the USSR. We also then learn that the USSR suffered the most casualties in the war, and took back most of Europe and ended in Berlin, so "obviously" the Soviets bear most of the responsibility for the war effort.
The thing is, that POV ignores a few fairly critical things, not least:
Lend-lease equipment sent to Europe accounted for a major portion of both British and to a larger extent Soviet supplies, and allowed for example the Soviets to shift production toward particular sectors while ignoring others. (Something like 409,000 American-built trucks and 47,000 jeeps were in service in the Red Army, meaning that was 450,000 less vehicles Soviet industry had to produce.)
the entire Pacific theatre of action (while Australia and New Zealand provided basing and some naval and air help, and the British sent their largest overseas fleet there in 1944, it was a US affair).