Thanks for the useful reminder. Your backup strategy should be based on the importance you attach to your photos. A pro will need and want more redundancy and will be willing to spend the time and money necessary to guarantee their survival. I'm an amateur, so I'm willing to run a little more risk. Nevertheless, I keep two copies of my complete archive on separate USB drives and all of the good stuff (and some not so good stuff) on SmugMug. If my house were to burn down, the main thing I would be lacking would be raw files, which are not supported by SM. But that would be the least of my problems.
One thing I would add to the discussion is that people do not pay enough attention to the process of restoring from backup. You should make sure that you (and your cloud provider) have enough bandwidth for you to restore in a timely fashion. Depending on your business requirements, it might not be OK for it to take a week, say. You should test it before you need it. I spent a career in IT and it was not uncommon to find shops that had been backing up their systems religiously for years but had never tested the restore, only to have it fail when they finally needed it.