So again, Bitcoin, Ethereum, etc - the base cryptocurrency of a blockchain is not meant to replace fiat currency. Honestly, it took me time to understand this myself. When I first entered the world of crypto, for a long time I was convinced it was too. And this is why almost all speculators (the ones who don't bother to do their own research) try to convince you with stupid reasons like fiat collapse.
So if not to replace fiat currency - what is the point then? Bitcoin, Ethereum, etc are meant to be as you call it, the "Itchy and Scratchy money" that are used to pay for the usage of the blockchain networks they power. So why fake money and not real money? Because you cannot go create a blockchain right now and make a fiat currency the base currency of the blockchain network unless you are the federal government. And since it is orders of magnitude more efficient to have a built-in mechanism as opposed to trying wrap something around the blockchain that pays node operators in fiat currency, the latter isn't an option.
Now with that known - given that governments are usually not the ones responsible for developing new tech and are also very slow to adopt new technology, could blockchain technology have taken off in any other way than it did? Venezuela tried to create their own cryptocurrency called the PETRO in 2018. And guess what - nobody, not even their own citizens adopted it. This is not to say the US wouldn't have better success trying to do something like this on their own - but we will never find out if you remove the talent pool capable of doing that.
Ok - so it cryptocurrency is meant to just power these blockchains, how will they benefit you, or me, or everyone? Here's a quote from Vitalik Buterin:
This quote doesn't mean the customer will be paying with Ethereum. This means the Ethereum network will enable the customer to interact directly with the tax-driver, both safely and securely. Without the intermediary of Uber, the customer gets a cheaper ride and taxi-driver gets paid more. The only requirement of the customer is that he has a small amount of Ethereum to open and process the transaction of his USDC over to the taxi-driver. And the chances are he may not even need Ethereum: some app will automatically convert his USDC into Ethereum that will be used to pay/process his transaction.
And this is the whole big "without intermediaries" selling point. You remove literally all of the bloat that exists in our current financial system: your bank, your credit payment processor, Uber, plus whatever is one the taxi driver's side, and replace it with one thing: the Ethereum network.
And this is just one of the many benefits.