Really 2-3%?Soviet Union got 10 billion supplies which was 2-3% of the Soviet GDP...
So in 2008 prices, Russia received about 138 billion dollars of Lend-Lease suppliesTotal Lend-Lease amounted $50.1 Bil. (612.88 Bil. in 2008 prices), of which 31.4 Bil. was delivered to the United Kingdom, 11.3 billion - in the USSR ...
And what was its GDP? I do not have Russia's GDP in the 1942-1945. But in 1939 its GDP was $ 417Bil., in 1941 - 359Bil. - according to Mark Harrison, The Economics of World War II: Six Great Powers in International Comparison
We would expect that with the loss of huge production capacities in 1941-1942 Russian GDP could decline in 1942-1945 - as compared to 1941 - not less than for a quarter, to the amount about $270Bil.
Thus, from mid-1941 to May 1945 the total Russian GDP was about $1.125Bil.
Lend-lease, thus, was not 2 - 3 percent of Russian GDP during the war between Russia and Germany. It was more than 12%! And your figure is quite incorrect.
And when we consider that in 1941 the USSR defense spending was 28% of its national incom (Harrison), and that the huge share of the Lend-Lease was on the needs of the Russian army and military industries, we will see that the role of the lend-lease to provide the Red Army with everything it needed in the war was quite critical
And if you said Stalin in 1942, that the Lend-Lease is not essential for Russia, I think he would just beat you with his fists for your words