I have used both and i come to know that native currencies are also very important and we can not say that native currencies are not important we have seen that native currencies are now using for transactions through banks and in future blockchain will take the place of fiat currencies.
I don't think it will reduce the value of real currencies, because the use of bitcoin as a digital currency remains not as much as the use of real currency. In addition, bitcoin is used by the upper middle class who master technology where not all countries legalize it.