Businesses pulling out of the UK based on the Brexit process is bad for the UK, and I'm sure this was indeed mainly motivated by N26's need for a UK banking licence, which is a costly and difficult process to go through. However, it's worth noting that they are pretty small in the UK (~200k users). They're very successful in Germany where banking is a very slow, difficult, manually run industry (from what I've heard)…
I was with hsbc for a year in the uk, I'd definitely not call it "generally very good" (ridiculous app and login infrastructure), but I have a sample size of one.
You can still send a payment from HSBC, for free, instantly, to any other UK bank account. You can also just about do most things in their online banking. This more than can be said for some other parts of Europe.