What a bizarre argument. Keynes wrote in the 1920s and 30s, so according to Diehl, did economics and finance not exist prior to Keynes? Was it all just a simulacrum until Keynes showed up and whipped out his General Theory? The map is not the territory.
This isn't even factually true. Crypto is in fact used in the real economy of places that have such bad monetary systems that crypto is much more stable. Look at Venezuela or even Ukraine and how much crypto is used there because the formal financial system is shambolic.
Crypto scams may be more common in the developed world where formal institutions are decent enough that the marginal cost of using crypto in the real economy is just too high compared to the legacy financial system.