> That gave us what was a stable-seeming, old "replace drives at 5 years, or you're getting risky" rule of thumb (unless you prefer to replace on failure, of course).
That's not exactly what this means. This is like life expectancy at birth vs life expectancy at current age. (which is the thing where people act like "only kings got old" in the past, when while there is some truth to it also doesn't mean "you would be dead by 30" when you already reached adulthood. The biggest difference we got regarding life expectancy at birth by far was doctors and nurses cleaning their hands, followed by things like vaccines for childhood diseases)
Manufacturing errors are likely to hit early. So replacing a drive means you might replace a perfectly healthy drive with one that will eat your data.
Just use SMART and you have a way better insight of how well your drive does than any such advice.
And also you likely won't run your drives in the same conditions as Backblaze, so things might vary in both directions.
There is shipping, storage, running conditions, series, manufacturing, and many variables. So you have a way better understanding of your drive than what Backblaze can provide if you just look at your drive's SMART data and run a self test.