Fiat currencies definitely aren't necessary, there is an increasing trend towards digitization of currency, and blockchain based currencies are just the next generation of this. The problem is that Bitcoin came out, and everybody treated it as the successor to fiat currency, rather than an incremental improvement on digital currencies such as Paypal and Skrill. I think that if Bitcoin was never invented, but somebody like Paypal had implemented a blockchain technology first, then we wouldn't be in the rivalry scenario that we're in now.
of course, all this time we use money as a medium of exchange for the products we want and need both goods and services. In the world of the economy, the exchange tool has several other names, namely the medium of exchange, and that is the characteristic of each country. If it is associated with crypto, there may be a little discussion.