Depends on the quality of the archival media. Magnetic hard disks aren't without their own failure modes. The magnetic signals on the disk eventually fade causing errors. Motors and arms fail. Cosmic rays flip magnetic state. Or just stray strong magnets if you don't store it right.
Really good archival optical media isn't susceptible to the same cosmic ray it magnetic fade while reducing the chances of disc rot or delamination.
Stray strong magnets haven't been a problem for magnetic hard disks for 30 years. I don't think the fading of the magnetic domains on the disk is a problem over merely geological time scales either, though I'd be interested in finding out if I'm wrong. The mechanical parts are the big deal, and for recent disks (last 25 years) there are also concerns with onboard Flash or other EEPROM losing state.
Cosmic rays will eventually destroy anything that doesn't have an active repair process, including archival optical media, but the time scales are longer than when the Sun is predicted to swallow the Earth.
Really good archival optical media isn't susceptible to the same cosmic ray it magnetic fade while reducing the chances of disc rot or delamination.