I have mine in a RAID 5 setup rn because I was scared about that, but I definitely should set up offsite backups, it’s just so expensive
Inherently to inner copy it provides some redundancy.
Backups need more than one copy.
Constructing a RAID5 with 4 drives provides failover and recovery if one of the drives dies.
A real backup protects both against hardware faults and accidental deletion.
Within a storage array though it does provide redundancy at that level, and generally speaking most people don’t access a raid or NAS at a shell level only where they drop rm -fr’s
Separate and offsite backups are non negotiable, however running a raid 5 locally can greatly reduce storage rebuild/restore time, if a single drive fails the rest of the raid continues to work fine until replaced.