I think you're largely right, but I have one nitpick: microfiche, and other types of microform, are pretty stable, and only require a magnification tool to be h

I think you're largely right, but I have one nitpick: microfiche, and other types of microform, are pretty stable, and only require a magnification tool to be human-readable. They're pretty much the gold standard for efficient archival long-term storage of information. But as you say, stone and metal as well as acid-free paper made from rags or mulberry fibres have a proven track record for longevity.