Security is also about backups. 3 Replicas 2 Formats 1 Offsite location

Yep, that's right. In theory you could share the encrypted DB with the public and not degrade security. (Still don't do that though...)

I just don't want any unauthorized persons anywhere near my vaults in general. I also see my vault as a critical service that requires high availability, and I know enough about system administration to know that my network and I are not qualified to provide that.

Let's say I have an unupdated patch and my server is now vulnerable.

This could really happen. I have work and life to worry about and I might not notice.

This vulnerability, could be in the BW instance itself (say the web server or the backend itself), or in the server itself (say an old OpenSSH version), or another service (NextCloud instance hosted in the same server under a different subdomain).

So, first we see it's a big attack surface. In any of those entrances an attacker could gain access to my server and with it the vault. It's a short way from there to install a keylogger on the website where BW is hosted, and get my master password ¯_(ツ)_/¯.

Now take into consideration that I just sat a couple of minutes to think about this, and I'm not a professional in cyber security or web security. Neither blue nor red team. A professional, with more knowledge, time, experience and resources, could probably bring up much more things.