I would expect it to be a mix of both, it has to be more of an expense to run physical branches while catering to a smaller market. But I would be amazed if they don't also blow those figures up beyond what's required to cover those extra expenses just because people have no real alternative to switch to. The largest bank had record profits for the last 3 years straight, and I'm not convinced it's just an inflation artefact.

Haven't heard of any postal banks, but digging a little it seems like we did have at least one... which merged with a commercial bank a decade ago. Sounds about right.