[dsacco]

There are two points you did not mention which make credit cards a more suitable medium:

1. Credit cards use a stable currency. Cryptocurrencies are not yet stable in price and are heavily impacted by speculation. If someone pays you in Bitcoin, you'll probably want to quickly convert that a conventional currency so you have a reliable store of value. You'll be doing a lot of de facto forex transactions as a result.

2. Credit card networks have far more transaction bandwidth capability than blockchains. Presently, there is no implemented cryptocurrency which can scale in the same way VISA and MasterCard have. This could change in the future, but I have doubts about it changing without trading off all or most of the "decentralized" component (at which point, why are we bothering?).

I think it's debatable that cryptocurrencies beat out credit cards in fees because they're fundamentally incomparable right now. Bitcoin is the most mature cryptocurrency, but it doesn't have anything resembling a mature ecosystem. It is not widely accepted, and you cannot directly use Bitcoin as credit. It doesn't have consumer protections like credit/debit systems do. There's really no telling if it would remain competitive with credit cards after it scaled up to real usability. You can abstract away transfer processing fees to a distributed consensus network, but you dramatically slow down the entire system in the process.