I’m not implying Raid 5 on its own is a complete backup.

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.