If you are regularly backing up your personal data to your own hard drives, the only advantage you are going to get from also backing up to the cloud (besides simply additional duplication) is geo-distant backups. So you would essentially be prepping for a catastrophe that destroyed your onsite backups, and possibly backups that you keep within the area. A house fire won't do this, but a wildfire or significant flood can.
Most of those fancy cloud storage companies are simply re-packaging existing cloud storage services available from companies like Amazon. You can just signup for their cloud services yourself, and pay a tiny fraction of what others are charging. Agreed that they can snoop on your stuff quite easily.
Hard drives do fail, but if yours won't mount, you should be able to analyze them with some specialty software or existing system utilities.
Remarkably, very long term apocolypse-proof data archiving might actually be best accomplished by storing the data in DNA. Harvard Medical School has tinkered with this concept, storing 700 terabytes of data in a single gram of DNA. There's even some chatter about doing this on cockroach DNA, so that the data can survive widespread nuclear destruction.