I mean, does archive.org get away with it, though?
They have legal troubles not infrequently and they’ve lost at least one copyright case that I know of recently.
I doubt if you pooled all the Lemmy instances’ resources that they’d have the resources to fight a copyright case.
And do I really have to spell out how Google gets away with caching stuff?
Finally, “fair use” isn’t magic words that magically absolve you of any liability in all copyright claims. I’m extremely skeptical fair use could be twisted to our defense in this particular case.