"Not having a branch means a bank is useless" - hmm, First Direct do not have a branch, i have been with them for 2 years, excellent phone service and you can put cheques in via the App. I applied for a saving account online (took me 30minutes in branch at Nationwide a couple of years ago).
The traditional banks do not care if you leave, i left Lloyds after almost 30 years, not a single acknowledgment.
I place Banks in the same slot as Estate Agents and Travel agents having a branch, there is no business benefit whatsoever.