Gold has the properties of verification and pseudoanonymity provided by public/private key cryptography. That cryptographic scheme just encoded that capability into software and made it much faster and cheaper because you no longer have to melt it down. Gold has all the properties of Bitcoin while also being hard money. Bitcoin is superior to gold and basically every way, but it shares the same properties, but to a lesser degree. Bitcoin doesn't magically escape gresham's law simply because it better fulfills the characteristics of money.