To clarify, what file system is being used now?
Are you saying that even BTRFS would have been better than what you have now? (though inferior to ZFS)
Or that you are frustrated that you have BTRFS to deal with now instead of ZFS?
I ask because I have been using BTRFS on a backup server and it has been working well for me (I think). About to set up another server for a client and considering using BTRFS for that, too.