Reversibility could probably be added on top via smart contract if someone wanted to provide the service, and people trusted the third party.

But you can't make a trustless exchange on top of a custodial framework.

Base layer has to be trustless / permissionless; all manner of third parties can build all kind of things on top of that.

But reverse isn't true - if base layer controlled by small number of third parties; nothing built on top can claw back that control.

Well, if there is such a thing as _the_ feature of credit cards, it's credit, as in deffered payment. Reversibility has its pros and cons. Similar to censorship and centralization. Until crypto, you didn't really have a technological means to prevent it, so it being popular in the fiat financial systems doesn't say anything.

Depends on who you are. For me the features of a credit card all revolve around convenience and risk minimization. Convenience in that I don't have to fumble around with bills and coins. Risk minimization in that US laws give me far more protection from fraudulent uses of my credit card than fraudulent uses of a debit card (and stolen cash is just gone for good).

Only once have I ever use the deferred payment aspect of a card, and that was a 0% APR offer.

While true on some level, this is broadly incorrect.

The necessity for reversibility, and the inflexibility of being limited either to it, or some form of it, is indicative of an inherent, unfixable flaw in the system itself.

This flaw limits the systems growth, adaptability, and usefulness.