I think what worries the U.S. more is the likelihood of Pix spreading around the world. It’s such a great public program that I believe many countries will eventually adopt it, or adopt some version of it. In fact, AFAIK some places already have it, like Thailand and Malaysia.
Consumers like it because it is widely available and free, companies like it doubly so, and even governments like it because it helps to combat tax evasion and fraud.
Right now, the only thing that makes credit cards a better proposition is being able to pay without having enough money in the bank, and maybe enjoying greater protection from fraudulent merchants. But I believe even that will change in the future, to the benefit of Pix-like systems.
The returns/refunds can be handled offline by a mutually agreed facilitator that does not have a monopoly on the payment system. You can also have a legal mandate that all internet purchase, for example, should employ such a service, that charges a market fee and is then liable for making fair decisions.