Explanation
The losses of Germany on the eastern front are widely believed to be the most significant factor in defeating Nazi Germany and the USSR won the battle of Berlin, the final battle before the German capitulation. Thus Europe widely believed (for a good reason) that the USSR was the main contributor in defeating Germany. With the cold war the perception of the USSR became a lot worse in western countries like France and with increasing anti-USSR sentiment the view flipped to viewing the USA as the deciding factor. The USSR (and the Russian Federation today, even if its government is very anti USSR) viewed itself as the most important force in defeating Germany, especially because the USSR had the biggest amount of deaths. It is worth noting that the USSR was at least commercially allied with Nazi Germany until June 22, 1941 and there was an agreement between the nations on which parts of Europe each could invade and which where reserved for the other.
Well, USSR wouldn't have survived without US help. USSR contributed the most in terms of territorial gain and manpower spent, but they would not have been able to make it without convoys to Archangelsk and Murmansk. These convoys were packed with materiell, mostly from the US, but a lot from the UK as well. Western tanks were vital in the defense of Moscow and Leningrad.
So, an objective answer to the question can only be provided if "most of what" is specified.
Nuance matters. Surveys like these rarely allow for that.
Yeah, even Soviet leaders, including the legendary Georgy Zhukov, low key admit (I will get to that later) that if it weren't for Lend Lease, USSR may have been defeated especially during the pivotal moments in the first couple of months of the German invasion. The material deliveries from the Allies filled the gap while the Soviet rushed their industries out of the German advances and restructuring the Soviet supply chain. Since you mentioned the Allied tanks, the British tanks made up around 40% of Soviet armoured forces in the Caucasus, since the Soviets couldn't easily deliver their own tanks to the Caucasus after the land route was cut off by the Germans.
After the war, the Soviet leadership aimed to minimise the importance of the Allied material deliveries in order lionise their own effort and exalt the communist system. But unofficially, many Soviet leaders were thankful of Lend Lease in a hush hush and low key manner.
Wrong, Khrushchev was the first one to say they wouldve been defeated if not for lend lease, soviet leadership after stalin tried to be friendly with west and betrayed socialism. There is no concrete proof either stalin or zukhov said it. USSR wouldve sailed through even without lend lease, altho they wouldve been much weaker after war and wouldve taken more damage. Most of the lend lease arrived after battle of stalingrad