Obviously them can never be the same but the similarities is there, because we use fiat currency to purchase pizza and we also use cryptocurrency to purchase pizza, which is documented in forum that somebody purchased pizza with crypto when Bitcoin did not dominate like as it's currently, so since this analysis happened previously, so while can't us accept the fact that btc and fiat are correlated the only difference is the regulations.
It's not just about the rules. It also lies in the principles of operation and areas of application. Under the current systems of public administration, which operate in all parts of the world, fiat currencies act as the basis on which the functioning of the economic system of any state is built, and not just payment for goods and services, and there is no escape from this.
The more the Fiat or currency of a country increase its value is the more the economy told growing this use as basis of how strong and how weak their economic stand is.
Like in some countries that their currency is depreciating value that means they are losing their momentum and need to act fast before their currency end up losing the High value.
This happens in Venezuela in other part of africa as their money is now comes almost no sense in using at all , that is why they are converting in to cryptocurrencies nowadays.