None of what you’ve mentioned has anything to do with Visa and Mastercard. Visa and Mastercard are just payment networks, their whole business is literally just transporting transaction information from payment terminals to banks and payment processors, plus keeping track of all the numbers (which is pretty important).
Payment networks don’t provide credit or any kind of liquidity whatsoever, that entirely provided by the various financial entities that communicate via the payment network. The reason Visa and Mastercard haven’t been easily replaced is simple network effects, nobody wants to integrate with a payment network where there’s nobody to transact with.
I had no idea visa/mc didn't bear the cost of fraud. I remember Paypal almost getting killed by fraud in the early days, and I always thought of Paypal as basically replicating visa/mc for online purchases. I didn't realize they were doing so much more than visa/mc by assuming fraud risk.
I replied downthread but I used "value chain" deliberately -- there are lots of intermediaries of which the card networks are just one link in the chain -- and the statement above is about risk being borne (and value being created for consumers) by the entire value chain that is different and difficult/impossible in a FedNow-style immediate settlement model: https://news.ycombinator.com/item?id=46964968
Mastercard and Visa also use immediate settlement models and basically always have done. The settlement buffer between end parties is created entirely by entities that are all basically banks.
There’s nothing special about Mastercard and Visa rails that prevents you recreating all the functionality that the broader ecosystem provides, without Visa and Mastercard. Hell all of that functionality could be provided by exactly the same companies and banks that provide it for Visa and Mastercard networks.
Because mastercard/visa don't personally bear any risk they are very happy to process refunds and chargebacks in the customer's favor. It's not a perfect system, but it's much better than direct bank debit where the customer has very little recourse. There is also a significant privacy issue. Today my bank can only see the sum total of my credit card purchases but not what I buy and from which vendor. Amex can see what I purchase but knows very little about me otherwise. I like this separation, and I like that it's hard for the government to get a complete picture of my financial affairs. I know credit cards get a lot of hate (here and elsewhere) but as a consumer I think they're exceptionally convenient.