ivansalloum It might not export back to the backup server, which your correct being BTRFS snapshot based... however, having a full copy elsewhere is a mitigation strategy. There's nothing stopping you manually extracting the archives you've taken, rsyncing them to the app server and letting the backups resume as normal again.
This of course suggests both app server failed and backup server failed and your using your 3rd copy to recover from.
That said it could also be for long term storage, enhance backups have a limit before there recycled. You might need to recover an email that was in someones inbox from 6 months ago, that no longer lives on the email server, or within the backups that are shorter than that.