In my opinion:

Bitcoin -> Primarily -> Currency
           -> Secondarily - > Investment asset

Majority of the world have a reverse point of view here which is the main problem which needs to reversed through adoption rates going upwards with time thanks to technological developments(LN fully ready etc).

I my self one of those who do not believe that fiat will die because of the existence of bitcoin and other cryptocuurencies. I also have no ideas why some people believe that bitcoin will replace fiat in the future. Bitcoin is indeed was created as a way of peer to peer transaction but I think it has been changed since many people use it for trading purpose and investment purpose. I still believe that the number of people who use bitcoin as currency is smaller than the number who use it as an investment tool/asset.

Bitcoin won't replace any fiat, fiat is used to control the country's economic and decentralised currency cannot be used to do that, btc main idea is to help people got a better payment system, its not for replacing any fiat, in the article it said that the transaction volume of btc is half from PayPal I think the reason of this is because some countries banning the crypto usage, I think bitcoin got a bright future because it offers something unique, bitcoin can be used as investment and currency at the same time

there are always parrots that repeat any crap they read online but i believe that others do understand what they are talking about, it is just that their purpose is to hype things up which is why they chose those words otherwise they don't think fiat will die, they just want to say it so that people get hyped up and they can make profit. somewhat similar to those saying "bitcoin is dead" that want to buy it at cheaper prices.

I honestly have more respect for those who are skeptics with good reasons, compared to those enthusiasts that are enthusiasts in the first place just because they simply bought bitcoin(without knowing anything about it) and shouting "buy bitcoin! price will moon!" to people, without even being able to back up their claims.

About "BTC is future, fiat will die", people in the bitcoin/crypto space has varying opinions on this. Some think fiat will die, some think that fiat can be potentially backed by BTC in the future.

Really though, in my opinion, most of the skeptics are skeptics because of the technological gap(why most skeptics are of the older folks). They mostly have bad arguments against bitcoin like "bitcoin can be hacked because an exchange got hacked", "BTC is not scarce because forks increases BTC's supply", and the like.

The rise of digital fiat has nothing to do with crypto though. They share the same medium is all.

I would argue that this movement is even detrimental to crypto adoption because crypto's biggest selling point to the masses is that it's digital, and most of them couldn't care less about what goes on behind the scenes. They'll be able to send money to friends, family, merchants (which is all most people really care about) just as easily as they can with crypto. It's going to be harder to stand out.

bitcoin's biggest selling point IMO is that it's programmable money and its supply/scarcity is predictable. the truth is that most people don't (and never did) care about the economics underlying their money. they use dollars (whether cash or checks or venmo transfers) because everyone else does.

but there may come a time when bail-ins and bail-outs or outright currency collapses vividly illustrate to people the importance of distinguishing between unbacked dollars and hard money like bitcoin or gold. hedging against those possibilities will become increasingly important in the future, and that alone may keep bitcoin at the forefront of public observation even if fiat money keeps sustaining throughout this transition to digital money.

Well there have been more than a couple of those throughout history, but it seems that the greater public still isn't very conscious of the risks associated with putting all their eggs in the fiat basket. It would indeed be pretty huge for Bitcoin if they start to learn though.

I have come to accept bitcoin/cryptocurrency as a secondary currency in my financial life haven known that bitcoin can not replace the traditional financial system like faint paper money, the blockchain is advance technology in the world financial sector despite the fact that blockchain base currencies are still new and have not been adopted as a legal currencies but with time this is going to be achieve because the blockchain smart contract transactions is what the world is waiting.