This is my other thought. Bitcoin in the first doesn't have the plan to replace fiat. Fiat is fiat and it can be replaced by bitcoin because in other ways bitcoin is bitcoin as well which can not be replaced by fiat either both are unique, both do have advantages and disadvantages as well. But they obviously are comparable that makes their differences.
They are both unique, that's correct, but it doesn't mean one can't replace another.
In some countries, people don't trust their own fiat at all and use USD instead. So if one day people don't trust USD anymore, they will then choose another they trust most. So it is possible they will choose Bitcoin if they find they can't find a better alternative.
It is all about trust.