regarding your comparison between a windows folder and localstorage feels a bit exaggerated.
yes, the Chrome team really fumbled it. and yes localstorage and important data should be mutually exclusive.
Local storage and/or SQL DB were touted as features for exactly this use case. That Google did not consider their persistence as that important for the release is perhaps not surprising for a company used to storing all your data in their cloud (not claiming they did so knowingly, just that it's probably in their culture, just as in your comments above).
but unfortunately i don't think your average user has any idea about what you wrote.
It seems like we could say "don't trust this" about any aspect of any platform. Categorizing every application as "really important, don't update the UI until securely written to three AZs" and "totally ephemeral purge every minute" excludes a lot of stuff in the middle. Sure, nothing made by humans is perfect, but many things could be improved. One improvement to localstorage would be to simply not delete all the data.
localstorage disappearing overnight IS a bug. If I put stuff in My Documents folder on Windows and Windows decides to delete it, that IS a bug too. You could argue that I should have backups, and you would be right, but that's no reason for Windows to delete my files, and that is no reason for me to never use my hard disk.