> Setting aside the LLM topic for a second, I think the most impactful way to preserve these 2 goals is to create torrent magnets/hashes for each individual book/file in their collection.

Not sure that's the case. I fear it would quickly lead to the vast majority of those torrents having zero seeders. Even if Anna's Archive is dedicated to seeding them, the point is to preserve it even if Anna's Archive ceases to exist, I think. Seems to me having massive torrents is a safer bet, easier for the data hoarders of the world to make sure those stay alive.

Also: seeding one massive torrent is probably way less resource intensive than seeding a billion tiny ones.