N26 is German. Revolut is London based but has an ECB license.
Yes, the SEPA scheme is old and working only during business days according to the TARGET2 calendar, but you definitely can process a transfer within a couple hours (my online stock broker does).
It creates a burden for people in that they have to do more paperwork. That time could have been spent on productive economic activity instead.
On another level, why should the state have a list of my accounts at all? It already sees all the accounts at banks within their territory. They don't need to concern themselves with accounts outside their jurisdiction.
In the context of income taxes, it should be enough to report total earnings, regardless of which specific account holds them.
The N26 app is garbage. Revolut is OK, but it's a money changing service, not a bank. I did a transfer from the Revolut account and it took 3 days. Topping up is fast because it charges your card, rather than doing a transfer.
The Transferwise borderless account is pretty good, at least I much prefer it to Revolut - since SEPA transfers happen same day, the app is better and the debit card is free.
Also the SCT inst scheme has started being rolled out.