how often do home hard drives fail?
They only need to fail once for something you have no copy of...
Also I am pretty sure they fail 100% of the time your laptop is stolen and/or there's a fire in your house that melts your HD. Are you saying houses do not catch on fire? That laptops are never stolen?
Your plan is lunacy. Backups aren't about any one unlikely thing, they are about a world of unlikely possibilities weighed against the loss of many things (even if virtual) that are literally irreplaceable.
does the average user still need "cloud backup"
The "average user" needs those things more because they do not have as deep an understanding of what will and will not be lost if the device breaks or vanishes.