I don't get your argument. If something doesn't work on the small scale it certainly won't work on a large scale. That's exactly my original point about managing global finance
It shits itself on the large scale.
Just like how trying to run an economy like you do a household results in the great depression.
They absolutely do.
Fourier transform multiplication methods are a terrible idea if you run them on numbers that aren't hundreds of digits long, but the only way to multiply truly large numbers.