Lend-Lease was only about 7% of overall Soviet war expenditure. Did it help? Yes, Soviets acknowledged that post-war. Was it decisive? That’s up for debate. Did it “defeat Hitler”? LOL.
That’s basically what you get if you don’t properly teach history. Idk how it is in France, but in the US I’d advise people to read Howard Zinn’s “The People’s history of the United States” to undo government brainwashing even partially, for just US history. I’m not sure what I’d recommend for history of the world, I have not yet seen a text that’d fit the bill.
On the other hand, I guess the change of perception is due to Hollywood.