This is also surprisingly easy to do with tape - simply leaving an LTO tape on its side can push failure rates to significant levels within a year.

If you care about data there's no substitute for multiple copies which are regularly verified. The idea that you can leave something on the shelf and expect to reliably read it is a dangerous myth. If you care about archival, build a system with the staffing and procedures needed to make that happen. This is enormously easier and cheaper to do with spinning disk below a certain level but if you have enough data the lower media cost of tape will balance out the increased overhead.

Do you have a source for that? I'd not heard of that before, I'm now interested to know what % the failure rate increases by

I'd never heard about that before, either (not having had tape storage as a primary job), but a colleague was quite surprised by 20-30% failure rates for tapes first used within a year and asked our drive vendor about it. At the time, there was nothing mentioned on the media we bought and the tape vendor didn't have any official docs but the drive technician we dealt with said that it was well known among the support group - apparently a lot of customers either didn't know or didn't assume it'd be so dramatic.

They don't mention the rates though

A single disk certainly is bad for long term archive. But when you have thousands of disks and use multiple copies for all data with some fancy error correction you can still get extremely high reliability, you just need to calculate in the expected failure rate.

The best part about a robot is that you can take things out of a library and move them to a somewhere without power or epic cooling.