Value of anything only exists in the minds of humans. No value is inherent to anything. You’re absolutely correct that gold isn’t fiat. But gold could absolutely be used as currency. Its in circulation and used as a medium of exchange. You’re also right that crypto is a currency. But its not a fiat currency. Crypto and fiat are both mediums of exchange not backed by a commodity. The key distinction is that fiat also relies on trust from the issuing institution.
I should have clarified: the revolutionary part is that through the possession of data (private keys), users are able to lay claim to their units of cryptocurrency.
Monopoly money is issued by Hasbro (private institution), can be fairly easily counterfeited, has little to no acceptance outside the context of a board game, and there’s no upper limit to how much can be printed. On top of all that: there’s no cryptographic way to prove the validity of Monopoly money and it can’t be transferred across the planet as easily as sending an email.