Topics like this encourage the comparison between fiat and btc instead. But yeah, comparing two different things and different purpose is pretty useless.
But Fiat and BTC have the same purpose, yes? BTC main purpose is being a currency that enables freedom of transaction where there is no need for third party. it was created to patch the flaw of fiat currency and enable currency be sent without intermediaries and without boundary. So we really can't avoid comparing this two Fiat and BTC because at some point they have the same feature.
bitcoin goes up and down and it is the same thing with USD, one cannot really survive without the othe,r I know many people will argue that this is wrong but the majority of Bitcoin holders get into Bitcoin using Fiat currency.
The only currency I won't be getting involved with is CBDC, because this currency is going digital and privacy first, and I won't be surprised to start hearing how people are getting spied on because they use CBDC to fund something.
Well, as we can see, we still need fiat currency because Bitcoin is yet to be accepted in most local market. We can't buy anything if we go shopping and there is no store that accept BTC. So I agree, that we still need to have fiat currency even if there is high inflation out there.