The way I look at it is that cryptocurrency is basically a security with no real use, but it can store 'value' in the same way those NFT things stored value for a while. There are more bullshitters for crypto, so they'll keep that hype train going longer, and you can semi work it to get some profit by buying the security low, and selling it high.
There was a post a while ago about how around something like 2020 or whatever, with billions invested in it, and with huge amounts of power/electricity going towards it, bitcoin had something like less than 10 transactions per minute globally. Like it's absolute dogshit when ti comes to transactions, in part because it's not a currency despite its name.
Currencies need to depreciate in value via inflation -- crypto tends to just store value and go up / down solely on its isolated demand as a nebulous concept. In fact, one of the bragging points from cryptobros is often this misguided notion that crypto is a hedge against inflation -- as that 'benefit' basically disqualifies it as a proper currency. If you get $1000, and that $1000 is able to buy you some quantity of goods, you need that money to be able to buy less of those goods in the future in order to encourage people to actually use the fucking thing. If you had $1000, but were almost assured that it would be able to buy twice as many goods in the future if you just held on to it for a bit under your mattress, you wouldn't spend the money... ever. Sorta like those crazy early crypto experiments where uni students were given like 25 bitcoin to see how they'd spend it -- and a bunch did exactly what you said in your opening bit, bought pizzas (you could at the time). Bet they would've preferred to buy a bunch of houses and sports cars later on, if they'd realised how popular the fad would get. Bitcoin only tends to go 'down' in value when people completely exit the currency, so it's not a valid currency.
I think you're generally right in your note about it needing to be exchanged. The whole point of currencies is that you don't want them to sit idle under someone's bed. Banks/Credit Unions provide savings accounts that pay interest, though typically slightly less than inflation. This is basically a function where because of inflation, you don't want to have your money just sit under your bed, you want to invest it in at least a savings account/term deposit -- but what's actually happening there, is that you're committing your money to the financial institution for a fixed period, and they're subsequently loaning that out to someone so that person can buy a house (typically) -- and then their payments on that house, is what generates your interest earnings (and the banks profits). The house itself is a security, with a general stable/safe valuation, so if that person can't make their payments on the house, the bank can foreclose, sell it, and still pay you your interest. So your savings are generally very safe -- especially, frankly, with simple/smaller financial institutions that aren't trying to do fancy bullshit / aren't doing any higher risk wealth management type back end tricks. Main point being though, that because of inflation, even people who have 'too much' capital, put it into the market, and it generates economic activity as a result.
Crypto, being a security, doesn't behave too well in this situation either -- in that you can't realistically hold a security and pay interest on it based on being able to use that security to fund other economic activity. Sorta like if someone hands you 10 shares of a stock (which has a variable price), and you've gotta figure out a way to pay that person back 12 shares of stock in a year, buy giving those 10 shares to someone else. What if they don't want shares of that stock? What if the stock price goes down, or up, significantly? There's just an absurd amount of risk, that would be considered wildly untenable for something like a person's core savings vehicle. There are some "interest paying" crypto type accounts these days, but that's a whole shitload of financial shenanigans and cryptobro bullshit. Cryptocurrencies are basically an economic blackhole.
And speaking of governments, anyone saying that crypto is useful because you can send money globally, is a moron. Banks/Financial institutions have the ability to do global money transfers with ease. The reason they can't/don't, is because of LEGAL reasons and regulatory restrictions from governments - it's not some technical restriction that crypto magically solves. Laws like "You can't let people fund terrorist groups". Crypto being able to do those sorts of things quickly is just a matter of them not obeying any of the laws or regulations from governments. That's not a 'good' thing in general. Many of the recent pushes from crypto sorts to get places like the States to recognize them, are basically resulting in banks getting less restrictions -- which really isn't a win. Crypto shows up and is like "We like sending money to north korea, so you gotta remove or neuter that whole know your customer thing for fintechs. Here Mr USA administration, we can pay you by buying millions of dollars of your personal 'crypto currency' to help with signing the bill. See, isn't it so much better to have no regulations/oversight on transactions?! It's win win!"
And the last negative I'll note, from my pov at least, is that the core mechanics of most crypto currencies is obfuscated and controlled by cryptobros. Financial industry people make money, but they don't make the sort of explosive, concentrated wealth that you see occur in crypto for the people who maintain those systems. That's partly because the financial industry is larger, and involves government components -- while crypto currencies are often just some techbro goin "let's fork bitcoin and stick a dog face on it and sell it to morons for big $$$$ then we can FTX it up fuckin in the bahamas with uggos!". It's the sort of obvious conflict of interest that they all try and bullshit their way out of -- one that typically doesn't exist in fiat setups, due to the multiple layers, and the role most govs fill in regulating things.