Fiat currencies are pretty 'vulnerable' to inflation and hyperinflation, but imo that doesn't mean that everything about it is bad or that Bitcoin is a better form of "money".
If you see it from the real perspective, you will be able to know that fiats are subjected to governmental manipulations, governments are the ones controlling the real value of fiats, not individuals. For example, the richest man in Africa is from Nigeria, there was a time this man, Aliko Dangote was worth $22 billion, but now at $10 billion, see what fiat has done to this man value in the world, he was the 23rd richest in the world as at 2016 but now at around 160 richest in the world. What caused it? Is it not governmental manipulations. That aside, dollar itself still depreciated while comparing to bitcoin specifically. Then what good side does fiat have than to use it to buy and sell because it is the legal tender.
That being said, the both forms of money is useful in our contemporary society
I have to reiterate this, what benefit can fiat give me than buying and selling? Nothing. I have my savings in bitcoin and some part in altcoins, fiats like dollar are still even better, while some/most fiats are absolutely useless.
but mind you that fiat currencies still remains a necessity, be it in our daily activities or to meet basic daily needs and other whatnots, they (Bitcoin & fiat) serve different purposes and diversifying your funds in Bitcoin and Fiat is the best option.
I can never diversify my funds on fiats, the only usefulness of fiats for me is spending, I only convert bitcoin to fiats anytime I want to spend, and if the spending can be made in bitcoin, I will prefer to use bitcoin, if the fee is too high and support altcoin with low transactions fee, I will choose altcoin. Diversify funds in this perspective means to save some of funds in fiats and bitcoin, this is not possible on my side as fiats are depreciating assets. As strong as US dollars is, it is still subjected to inflation, all fiats are subjected to inflation while those from developing and underdeveloped countries are subjected to hyperinflation, but the degree only varies according to the economic condition of each country of the world.
Fiats as nothing to be compared with bitcoin in terms of value and appreciation, fiats are depreciative asset while bitcoin is an appreciative asset. I hope this point is clear and remains the fact.