This is not a honest comparison. Books are mass produced and don’t rely solely on their authors paying hosting bills and willingness to not change stuff to keep existing.

Relying entirely on a single nonprofit (archive.org) to provide a honest snapshot of every cited link, at the time of citation, sounds much more unreasonable.

A lot of national libraries also undertake web archiving within their scope (e.g. under their national TLD) and I've sometimes found that they have items not covered by Wayback, but it's not as easy to request additions to it. The risk of having a single point of failure is certainly real, and it would certainly be nice for a coalition of libraries to maybe fund a second alternative and mandate the use of both, or something like that.