Just because it's in the name, doesn't mean it should be considered a fact or best practice in accordance with reality. I think this[0] reddit post frames it in the simplest way possible: "A backup is a copy of the information that is not attached to the system where the original information is."
There are many[1], many[2], many[3] articles about why "RAID is not a backup". If you google this phrase, many more people who are considerably more intelligent and wise than myself, can tell you why "RAID is not a backup" and it is a mantra that has saved myself, friends, colleagues and strangers alike a lot of pain.