I didn't bring it up because its not overly relevant to the question, since it doesn't explain industrial output. But, to address the Lend Lease, it was definitely useful and important, but I wouldn't call it over the top crucial to the soviet war effort. The most of the Lend Lease program in fact went to Britain, since Britain got 31.4 Billion worth of supplies, and the USSR got 11.3 Billion worth of supplies, so right off the bat lend lease provided more to the Western powers. Lend Lease was a mainly American/Canadian effort, Britain itself gave little help to begin with.
Next, Lend Lease gave the USSR about 400,000 jeeps, 12,000 armoured vehicles (most of which were Sherman's), 11,400 aircraft (this isn't all fighting aircraft, though almost 5,000 were fighters), and 1.75 million tons of food, and more. This, by US military standards, was enough to maintain almost 60 divisions in the line.
60 divisions is A LOT, yes, but proportionally, for the USSR, this accounted for just 13.3% of the USSR's military. A division is between 10,00-15,000 soldiers, and the USSR had over 6.7-6.4 million soldiers. If each division was 15,000 people big, then lend lease supplies could sustain 900,000 soldiers. The USSR had to provide itself for the other 86.7% of its military, or 5.8-5.5 million soldiers.
USSR industrial strength far outpaced lend lease help. Between the war heavy years of 1942-1945, the USSR made anywhere between 12,000-20,000+ armoured vehicles a year, with 1943 and 1944 being the most production heavy years. The USSR had over 25,000 tanks just alone at the very beginning of their war in 1941. In comparison, 4-5 years of lend lease aid was the equivalent of 1 good soviet year of industrial production. Lend lease never really supplied 60 divisions at a time either, lend lease aid is stretched over the years of ww2, and supported less than 60 at any time, 60 divisions is the figure for the total amount of aid given over all of the years combined. Not to mention that lend lease did not provide any significant amounts of soldiers, volunteers, or just men in general, so manpower remained a mainly USSR concern.
I don't partake in the "Oh USSR is so great, it did everything by itself!" circle jerk, if anything I acknowledge that the Western front significantly helped the soviets, since the Germans left huge, well equipped swathes of men on the western front in anticipation of an allied invasion in France and/or Norway. Men that could have helped swing Germany fortunes on the eastern front, or at least equalize it. But I think that Lend Lease, while very helpful and definitely inflection, didn't really enable the USSR, it didn't give them "most" of the tools needed, that was, as far as I'm concerned, a soviet effort.