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.
Actually pulled the plug on my UK ltd. pre-Brexit due to Bankxit...