This is just factually wrong and has no credibly outside of a few extremely left wing economists and those believe it despite the economic research or because they have not studied it. The New Deal has achieved mythical status in the left wing version of history, but that is simply not an accurate depiction of history.
If you look at the numbers in detail, you would see that when the US left the Gold Standard, growth immediately came back, industrialist production skes back up. This is pretty clear pattern with all the nations who were under deflationary pressure. Leaving the gold standard (or adjusting the exchange rate) was the fundamental thing that restarted the economy.
It is pretty clear that the NIRA actually stopped the ongoing recovery and indsutrial production only outpaced the pre-NIRA level again when NIRA was declared unconstitutional. Why anybody would declare the total madness of this program a success is just unbelievable to me. Massive destruction of food, mass slaughter of life-stock to increase prices. Blue Eagle program to 'keep prices high' were exactly the wrong things after a deflation.
Contrary to popular history, New Deal was not some brilliantly executed Keynesian program. In fact it does not fit any economics logic at all.
The US had one of the globally worst recovery path from 1931 to 1939 of all industrialized nations. Specially consider how well the came into the situation compared to everybody else. Why this period is hailed as a great success, is because it was an incredible political success as FDR managed to totally rebuild the democratic coalition. That coalition remains to this day. Of course the left and specially democrats hail it as the biggest success in centuries, because it was politically successful.
And the claimed that it 'prepared' to US is mostly wrong. Roosevelt to his credit was smart enough to kick most of the New Deal idiots out of his administration going into WW2 and worked with actually sensible people and during WW2 and after the US actually removed the majority of these terrible polices and that allowed the US to recover far better then most other countries.