Yeah...I've never totally lost my main storage and had to recover from backups. But on a number of occasions, I have been able to recover something that was inadvertently wiped. RAID doesn't provide that.
Also, depending upon the structure of your backup system, if someone compromises your system, they may not be able to compromise your backups.
If you need continuous uptime in the event of a drive failure, RAID is an entirely reasonable thing to have. It's just...not a replacement for backups.