I think there is some difference between horse-car and fiat-bitcoin situations. Horse is obviously worse than a car, because you can only travel alone with a horse and you have no shelter in case of bad weather. Fiat has inevitable inflation and bitcoin doesn't. However, bitcoin is not and can not really be regulated by any government, whereas people mostly prefer some guarantees and stability instead of anarchy.
I agree with you also, I don't believe that fiat is already on an extinction level yet. Many still use it today in transactions to pay for goods and services that they need in their everyday life. Fiat is still needed to survive in this world so its not on an extinction level yet. Before it happen, there might be a crypto currency that is made by the governments to replace fiat and that crypto-currency is centralized I think.