Theoretically, bitcoin can beat fiats as it is technologically superior- the evolution of money is very dynamic.But on a practical ground, it is difficult to see bitcoin completely replacing fiats since fiats is based based on a model where government and banks control the flow of money and use it as a means to achieve government economic objectives.In that regard, fiats will always be in use because of government influence.
Governments have the ability to create instant demand for anything, they got genuine power to force that. Ultimately I believe in market forces and every nation is a servant of change that will occur with or without them, obviously its alot better to be ahead of that wave of change not caught up in the turbulence that follows.
Its possible crypto is part of that change but I agree nothing is going to replace FIAT completely. Just like FIAT has never actually beaten the old system of gold completely, sure its done a large part of that but even now we might see gold return. We can see the return of many alternate standards besides the current dollar reserve system, we can see a variety of FIAT alternates, commodity based exchanges and also crypto can be some part of that