I think they can't be complement each other because they are different things
Fiat is legal currency that regulated by government.
Bitcoin is investment just like gold , diamond,etc but as we all know that bitcoin has specality that act like money/fiat
yes, bitcoin will only be seen as an investment compared to fiat, because basically fiat is legitimate money, and has obtained legality from the government. besides, I am only sure that bitcoin can beat Fiat on the internet, because it has many advantages. well, we can only have a discussion, I think the development of both will be better in the future.