... 'size' is really not that important. What matters is the content, it's uniqueness and relative importance.
Libraries, even books (let alone literacy) during antiquity were rare and generally unique, remember, this is before the printed press.
The Library at Alexandria was a 'first-order' source of knowledge and wisdom, a place where 'intellectual luminaries' (i.e. big rabbis of the day) would have studied. Possibly every single book represented a unique bit of knowledge, and each one a historical artifact.
Losing the Library at Alexandria would be like losing 15% of all Universities, professors, all of their papers, textbooks, 15% of authors, playwrights, all of their works, 15% of all written history - basically most or all copies of their works, vanished into thin air, for all of time.
If the Library continued to exist in its fullest form, we may very well have much more of our history pieced together.
The Internet Archive is not even a 'second-order' resource. It's nice to have, and useful particularly for some historical reasons, but if it were to evaporate tomorrow, civilization wouldn't skip a beat.
There is no specialized, arcane knowledge there. Parts of the IA are of course really nice to have, particularly the news which forms a kind of historical record. But old copies of 'HomeDepot.com' and 'McDonalds.com' are just not that important.
We don't use the IA as a source of science, physics, fiction, students don't go to the IA to access authors' works or textbooks on orbital physics.
If the contents of IA were seriously valuable, then quite a number of parties would be interested in maintaining it, first of all, the parties being documented (if HomeDepot.com doesn't care about their 2006 web-site, then maybe it's not so important).
I support the IA and I would hope that it was even a kind of government-sponsored agency, but it's not an 'intellectual foundation'.
(Edit: changed from 25% to 15%, it's just a number obviously, but my point being 'it's some material share of the compendium of knowledge')