If we spoke about a Linux box, one that prudently ran ZFS, or XFS on top of LVM, it would be possible to make a snapshot before the diffing and sending, so that the snapshot would be indeed point-in-time. IDK if whatever macOS uses for the filesystem supports snapshots.

Otherwise, I think, restic or kopia are better for proper backups, and Syncthing for keeping a mirror copy. But the simplicity of this script in charming.