crypto indeed gives us the ease of transacting with various people in various parts of the world. but to replace fiat, I think it's very difficult. although crypto can overcome some deficiencies of fiat, it doesn't mean that crypto doesn't have flaws. a real problem, how do you as a seller of goods determine the price of an item using the value of a very volatile crypto currency? it will be easier to determine the price of an item using fiat. nothing is perfect from a technological development.
you are absolutely right. I was thinking the same. Fiat has a stable value which helps us to determine the value of goods and properties. while crypto is very volatile. for example if we say a Mobile phone price is 1 Eth when the ETH value is $200 but if the Eth value suddenly drop to $100 or increase to $500 then it'll be hard for both seller and buyers. that is where we need Fiat.