Harder, not impossible. I've only experienced one banking app that doesn't work (and I didn't try disabling the security for it). I have another AOSP without google services and it's a bit worse but half of the banking apps work. Uber doesn't.

Not sure where you live but in the EU I think you can ask for either SMS or hardware token verification for the bank website.

The most annoying thing for me is "magic links" apps send via email to login. I don't have email on my phone.