In addition rsync allows you to efficiently have several versioned snapshot style hard linked backup copies. Each snapshot looks like a full copy, but (almost) only takes up storage needed to store new or modified files since the previous snapshot. Even if you have RAID, you still need backups to handle user errors and mistakes deleting or overwriting data. And if you have good versioned backups, chances are that you don't really need RAID.
For commercial settings RAID may be needed, in addition to backups, to provide high availability. But then I somehow doubt any SBCs and USB3 connected HDDs are used.
However, rsync backups/clones are not enough, in themselves, to provide bitrot protection. Then further measures are needed. Checksums and so on. This may be relevant for long term storage or archival of valuable assets. Some filesystems with redundancy are able to provide bitrot protection.