> Cash is, after all, the only instant and feeless transaction method.

Bank transfers in the EU are instant, and there are no fees for personal accounts.

> Imagine I bought the car on Friday afternoon. The seller would get the money earliest on Monday.

No, the seller would get the money before they could even blink.

I have accounts at 2 unrelated banks. I have my online banking apps set up that whenever I get a deposit over a certain amount I get a push notification. When I use my online banking app to transfer money from my account at bank A to my account at bank B, I get an alert from bank B’s app to inform me of the money appearing in my account before the app from bank A has even shown me the confirmation screen that the transfer request was received.

This is true for any two banks in a SEPA country.