RAID is not a sensible substitute for a good backup system, as there are too many things that will take down both drives in the array simultaneously, including controller failure, power supply problems and even theft.
RAID gives you a degree of backup confidence, but only against a drive failure. To protect against the other issues you need backups, and if you have backups to protect against the other risks, you are protected against drive failure without needing RAID.
There are some performance advantages to some forms of RAID, but mainly, it's about resilience and uptime, not backup.