We're under fire! Yeah - under fire!! Those five thousand ships the Allies couldn't possibly have, as you say - they've got 'em! Yeah, they've got 'em!! - Major Werner Pluskat, June 6, 1944.
The process used was very crude, simple and inefficient so they needed to do it on a huge industrial scale. And only the US could do it on that scale.
You could call it "the dumb luck of nature" that something like an atomic bomb couldn't have been produced with, say, 19th century technology but that it could, barely, be produced by the full industrial might of a mid-20th century nation.
Which is to say that start-up producing amazing things in basements now certainly rely on the sum-total of previous industrial achievements, we don't how much some interesting bit of knowledge compared to those achievements could be leveraged.
If Wikipedia is to be believed, the US produced more M4 chassis (all vehicle types) in 1943-alone (21,231, admittedly a huge surge in yoy production) [1] than Germany produced of any single chassis type during the whole war (most numerous: Pz III at 15,747 total) [2].
[1] https://en.m.wikipedia.org/wiki/American_armored_fighting_ve...
[2] https://en.m.wikipedia.org/wiki/German_armored_fighting_vehi...