And how could social and political arrangements fail to determine what happens in the long run if they determine what happens in the short run? Do social and political factors suddenly stop causing economic phenomena at any point in the lead-up to the long term? The illusion that the economist has a transhistorical, scientific perspective on economies belittles the roles of sociology and politics. In the long run, these factors supposedly cancel each other out because a simple equation predicts the quantity of money in an economy. But what makes the equation work? Psychological and political factors, evidently, the same ones that would be manifest in the short term as in the long run.
And who determines how long the long term should be? Will this quantity theory of money apply ten thousand years from now? Of course, it hasn't been around long enough to be tested at that scale. But suppose it turns out that capitalism helps indirectly to kill off our species within that time frame, because of the very psychological and political forces that capitalism/modernity exacerbates (including consumerist narcissism, Big Tech infantilization of the masses, plutocracy, and so on). In that case, this pseudo-physical pretense that money has a "velocity" will have been bogus all along.
So the dubious analogy with physics is hiding the messy psychological and political factors that determine what go on in an economy. The talk of how these factors wash out in the long run, along with the weird rhetoric of money's "velocity" makes capitalism look like a system that can survive in the long run. That's an ideological advantage that benefits the winners more than the losers in that system.
The pretense is that capitalism has its own nature, so we should let it be. The pretense is that it works all by itself, like Newtonian mechanics, that it doesn't need to be saved by central planning. Every time the orthodox economist makes an economy seem like something physical that likely lasts in the very long run, I'd say this scientism is obscuring the more unstable psychological, sociological, and political factors. And yes, that still applies to your example of this quantity theory of money.
