I consider that similar to a bug in the browser or the operating system. Should the bank require that I only use specific browsers or operating systems? In fact any program I install on my computer could have a vulnerability, or be malicious and thus lead to my password being stolen. Should the bank require that I not install any programs except ones they specifically permit?

The bank should also consider which is more frequent: user account compromises due to weak/reused passwords, or user account compromises due to password manager bugs.

Then banks should recommend a good password manager. It's on them to make their users happy after all.

One part of that is a proper risk analysis. Password reuse and weak passwords are much bigger risks than a rouge autocompleter.