This is contradicted by the entire economic history of the 19th century, when the industrial economies all had robust growth/investment combined with long-term

This is contradicted by the entire economic history of the 19th century, when the industrial economies all had robust growth/investment combined with long-term secular deflation. That's not to say there isn't an argument for inflationary currency. But that argument is centered around the ability to conduct counter-cyclical monetary policy to stabilize the business cycle. But it's silly to say that deflationary assets are literally impossible to serve as currency, because we have actual historical evidence of deflationary currencies.