If being extremely charitable, USSR might've won without American Lend-Lease but the cost in lives doing so will have been even more astronomical. Without any Lend-Lease at all USSR would've been so utterly fucking dead.
Former members of the USSR are dealing with an absolutely awful demographic collapse in great part due to the war that happened. Now imagine the war that could've happened if the US didn't give them a fuckton of stuff to give their men a fighting chance.
Hell, one of the main products supplied to the USSR was the Studebaker US6, which considering that the competing GMC CCKW was accepted into US service, was almost entirely made for the Soviet Union. It was so good that I've read about how by 1944, the domestically produced ZIS-5 was relegated to a reserve role in favor of the US6 AND the Soviet trucks produced after the war (namely, the GAZ-51) were all based upon the US6 instead of the ZIS-5.
Supply trucks are greatly overlooked in favor of tanks, which is why the usual commie bullshit I hear is "hurr-durr, 50 thousand T-34s with only a few thousand Shermans in Soviet service" whenever they try to downplay the importance of Lend-Lease. But supply trucks are the backbone of logistics in modern warfare and, as Stalin's letter to Studebaker showed, the trucks themselves are the lifeblood of logistics, which the Soviets knew as well. They didn't need more tanks per se, they had enough of that - they needed reliable, capable trucks that could get men and supplies from point A to point B.
Even rabid America (and general Anglo, in this case) hater Frenchie faggot Charles de Gaulle was verbally pimp slapped when he demanded the withdrawal of US troops from France and was met with the famous "including those in your cemeteries?" retort. Like nigga, your ass was given a cozy radio showhost booth in London, your army was given a fuckton of Shermans and small arms, American soldiers died in the thousands so your frog-eating ass could march into Paris after Uncle Sam already did the heavy lifting for you, the fuck you hatin on Anglos for?
The Soviets themselves (trust me, my grandparents heard some wild propaganda back in the Eastern Bloc) didn't hate the US nearly as much as these "Lend-Lease didn't matter" cunts. If anything, they feared Uncle Sam, since they
knew how capable America was: they've seen it bodyslam the Imperial Japanese Navy, bomb the ever-loving shit out of Germany, annihilate Hiroshima and Nagasaki with never before seen weapons while supplying half the world with equipment, from China to the UK. Not in some Soviet-style "here are outdated, beat-up T-34s we had in stockpile lmao" way, but giving proper, up-to-date stuff like M18 Hellcats to China during the war.