Maybe bitcoin can not replace fiat, but surly it can complement it.
Because its easy to transfer bitcoins to any place in the world and convert them back into the local fiat.
I agree that bitcoin cannot replace fiat. One of the things most crypto people is thinking that, this stuff is the trend, we should replace the trend before it then. But it won't be happening because of several reason. Major reason is that the decentralisation feature of it. It is against the concept of the government where all they want is that centralisation so they can control everything.