From my practical observation: People will go to great length to avoid dealing with a crappy UX. That can include falling back to "YOLO, I'll just use the same password everywhere" if the password management process is sufficiently atrocious. So I'd say good UX is part of the security concept, bad UX will compromise it.
Maybe, but a good UX goes a long way to convincing people to use the solution. The best security solution is the one you actually use.
People are reusing passwords and writing passwords down on post-its specifically because they haven't found sufficiently UI friendly options of password management. Regardless if that is out of ignorance of available options, UI not being friendly enough for them, or some other technical hinderance.
A compromise isn't weighing between an ideal scenario and your current situation. A compromise is finding an optimum between value extremes in acceptable real world scenarios. An ideal security extreme is a disconnected system, but that's never something you can compromise towards since the comfort/usability reaches 0.
You're trying to move security up by getting users away from pass reusage and post-its. In this case added comfort happens to also be increased security.
Any app that gets updates is vulnerable to that type of attack.
This approach is exactly why the vast populace has essentially no security. I'd be glad if my parents were to switch to last-pass, as it is so much better then weak password re-use schemes.
I'd say that compromising security for comfort is a given, its guaranteed to happen. The best strategy here is to make sure that users will have the most security after the compromise.
I think a lot of people feel uncomfortable giving a proprietary product access to their passwords, and feel more comfortable doing the copy-and-paste themselves. But compromising security for better comfort is not a very good strategy.
Keepass has a third party Firefox extension that does this. Bitwarden is open source and has their own extension that does the same.
This seems to me like a great argument to avoid all cloud based providers and their mobie apps. Especially when opensource, time tested, self-hosted solutions exist.
You seem to be more concerned about UX than security. Compromising security for better comfort is not a very good strategy.