We've now conflated two important distinctions into a single subject here. Functional resilience and long term data integrity.
I solve the long term data integrity problem by doing nightly snapshot delta's of my whole machine and my wife's machine (to a rasp pi with an external drive at a buddies house). Granted that's a single point of failure, but it's out of house in case my house {burns down, get's robbed, etc}
However, that doesn't fix the near term issue of me busily working away on a project when boom, my drive fails and suddenly I'm sitting there looking at a paper weight. That sucks. Having that happen to me once was enough for me to say screw it, I'm buying two drives and mirroring them using the motherboard raid software (which md supports) and it's a non problem. This solves my functional resilience.
raid is not a backup, what is gives me is resilience. Would you rather spend tomorrow recreating your machine from install media and backups, or simply swapping the drive out and suffering a background sync?