1 in 40,000 customer devices experiencing a failure annually is considerable better than 4 9s of reliability. So we are debating whether going from 4 9s to 5 9s is worth it.

And like, sure, if the rest of your stack is sufficiently polished (and your scale is sufficiently large) that the once-a-year bit flip event becomes a meaningful problem... then by all means do something about it.

But I maintain that the vast majority of software developers will never actually reach that point, and there are a lot of lower-hanging fruit on the reliability tree