Bitcoin and fiat currency is different in term of its a value because the bitcoin is decentralized and the economy of a single country cannot manipulate their funds is the money is more on digital and they cannot control. In my opinion, the bitcoin cannot replace the fiat currency because each country must release their own currency to identify and makes a different value when you are going around the world if we are talking about bitcoin it's fixed all over it cannot be that the bitcoin price Is 7k on USA and 9k on Europe.
We always say that bitcoin is an alternative currency, yet we don't use it as an alternative, maybe for some they do but most of us? hell no. We are afraid of the volatility, that's the truth.
this is the important point. bitcoin can be used as an alternative payment. But, it is not effective enough for some people. For one thing, because of its high volume, the price tends to change, making it less appropriate to use as a tool for determining value. Bitcoin is more effectively used as an investment tool and commodity trading, its volatility is used to get profit. This all depends on the point of view of each, can not be forced, as needed.
Right now the bitcoin is one of the things that people would like to adopt because they want to make easier transactions and also it may lessen the hassle right now the gambling platform and even the online shop is accepting the use of the bitcoin as payment but still, there are some people want to use the fiat currency. Still better to have the bitcoin and fiat currency in a separate aspect.