I'm surprised if you had something like plain plex on a bare debian install break. It's been rock solid ime. And many people do do it, *arrstack has a huge community. I think lots of people experience some sysadmin-type issue and then extrapolate that adding all these extra apps will linearly scale up the likelyhood of breaking. But the extra apps are dead simple and do not cause additional issues ime. There is practically no startup config for most of the stuff (sonarr/radarr/prowlarr) save for a config volume mapping - the docker-compose for those looks extremely bare. And all the addon components are widely updated automatically in the community and I've never so much as seen a complaint of a failed update (I'm not even sure if there are any kind of schema migrations, never seen anybody get a corrupted DB). Sure plex DB does get corrupted for some people but I suspect there is some exacerbating factor since I have never had a plex DB issue - perhaps it's more prone to issues for people using DVR, plex plugins, etc. I just use a stock plex setup with movies and TV shows and the default metadata settings. Never had an issue.

I guess to put it more concisely, adding the *arrstack doesn't really add many (hardly any?) additional failure modes. All the reasons it might break are the same reasons that the plex or the whole system would break. If your system runs out of storage, it might break. If you change the file permissions of some config or data folder, plex might break, and so would arrstack if you chmoded the config files so it couldn't read it. If you can keep plex running on a bare OS, adding arrstack is not really more work other than the initial setup.