I believe Vaultwarden keeps data encrypted at rest with your master key, so some of the problems inherent to hosting such data can be mitigated.

I can believe this, and it's a good point. I believe Bitwarden does the same. I'm not against Vaultwarden in particular but against colocation of highly sensitive (especially orthogonally sensitive) data in general. It's part of a self-hoster's journey I think: backups, isolation, security, redundancy, energy optimization, etc. are all topics which can easily occupy your free time. When your partner asks whether your photos are more secure in Immich than Google, it can lead to an interesting discussion of nuances.

That said, I'm not sure if Bitwarden is the answer either. There is certainly some value in obscurity, but I think they have a better infosec budget than I do.