Pland D just made a very strong point.
While there is no doubt the massive human resources available for the USSR played a vital role on soviet victory, I also agree, from what I have read so far, as well from the accounts of veterans, that the USSR, by the time of the German surrendering, was an exahusted and bled to death nation.
That their human resources were massive has never implied they were endless; no nation on earth, no matter how big it might be and how large its population is, can take what the USSR took during WWII without paying a very high cost.
During Operation Bagration (June 1944), the massive summer soviet offensive which pushed the Germans out of the USSR for good, there were countless reports from the frontline troops, informing on how bizarre the red army was becoming.
Along with the large numers of T-34s, self propelled artillerie regiments and massive artillery barrages, the soviets were sending big numbers of children, women, elder and impaired people; lots of them were hardly armed and countless were barefoot!!
I recall reading on several books, General Erhards Raus (commanding a Panzer Korps -forgot the number-) during the summer of 1944, reported that among the soviet prisoners captured were women who did their laundry only a few weeks ago in Minsk.
This seriously contradicts the commonly accepted version of a "totally new, fresh, lavishly equipped Red Army, with renewed tactis to destroy the Wehrmacht" emerging from the USSR during 1944.
History has managed to depict the soviet union recovered from the utterly brutal and nightmarish defeats of 1941/1942, just like if coming back from a series of "minor" setbacks and mishaps.
Indeed, after WWII the USSR was a world power. But the price and the consequences of WWII on its people have hardly been assessed so far.
This, alongside, with other elements, comprises the overall notion on how helpless the USSR would have been without foreign/allied help.