Well that would be the description of the community, but the actual rules section doesn’t say anything about privacy/control.
So at the end of the day Plex is self hosted (you run most of it) so it should qualify. It might not 100% match the spirit of self hosting it does still meet the definition.
You can argue most Jellyfin/emby installs have the same problem because most users are still are dependent on external services because of things like metadata plugins.
And on the privacy front those plugins aren’t any better than Plex. For instance The Movie DB which is the primary movie and TV metadata provider for Jellyfin has a privacy policy that clearly says they will use and share any interaction you have with the site including location and personal information. They almost certainly keep track of what is in your library. They don’t have a user account for you that they can use to track across IPs, but if your ISP keeps you on the same IP for long periods of time they have a good idea of what you are watching.
You can run Jellyfin without those plugins enabled but unless you want to build/collect manual nfo files to import that data you are going to have a subpar experience.
Same problem for the **arr stack since they need metadata as well. Some of which go to different providers so you are giving out that information to additional parties (i.e. Sonarr goes to TheTVDB which has a similar privacy policy).
You can configure the arrs to write out nfo metadata and have Jellyfin consume that so that at least you aren’t giving away your info to two external parties.
Btrfs raid5/6 support is unstable/experimental and cause some serious issues in the past, so it isn’t really recommended.
Since you only have 4 drives you could do a pair of mirrors with btrfs, but you aren’t guaranteed to be able to handle two drives failing (depends on which two drives fail). So zfs with raidz2 is the best protection you can get, and it matches the capacity you would get from mirrors.
Rebuild time isn’t great, but you would need a second drive to fail plus at least a read failure on another drive before you have issues.
A bigger question would be how soon would you have a replacement? If you already have a spare on hand I wouldn’t worry about rebuild time at all, but if you are expecting to wait potentially weeks for a warranty replacement your chances of the second failure go up.
Even if you had a second failure and additional read failure is unlikely (how often do you see read failures when you run a scrub). Combine that with your backups… You should have very little to worry about.
If two drives failed and you ran into a couple of sectors that can’t be read ZFS continues to operate just fine, except for the failed file. The file with the failed blocks shows up in zpool status so you know exactly where the corruption is, and you can just copy that single file from your backups and everything is back to normal.
If your files are mostly WORM files like media/documents then your backups cover you really well and copying a file or two from backups isn’t a concern. Vs if you are running virtual machines or DBs that are writing to their virtual disk constantly then you would start to worry about how much data you lose by rolling that file back to your past backup.