IIUC Sci-hub has scooped up science docs through a good enough UX that it was able to leverage the goodwill of science folks to upload docs (plus whatever other methods it has used to scoop up docs), and it uses a public blitzkrieg-style distribution mechanism. I.e., I guess if one had a big enough harddrive and a fast enough internet connection, one could start downloading the lib right now and see if they win the race against the copyright holders.
On the other hand, the What.cd/Redacted approach seems to use Bittorrent ratios to create a private-tracker economy. New users get a few gigs free download on joining. But apparently because a) there's a 1:1 upload/download ratio, and b) a few first-mover fat cats are sitting on enormous ratios, this means there is a scramble by everyone else to upload new FLACs to build up their ratio so they can continue to be able to download FLACs. It seems that would mean the library-in-its-entirety cannot be easily replicated at will. Yet the tracker was apparently already nuked off the internet as What.cd and reappeared later as Redacted. Was any data lost between the two services?
Oh yeah, there's also apparently another approach in rutracker, which seems to be blitzkrieg to add content and publish, at the (apparent?) cost of quality of content.
It's really a shame that the nerdy, completist domain of digital archiving through torrents isn't covered by fair use. Perhaps we could exclude the most recent 10 years of music so that the hopeful young musician streamers can get paid a few hundred dollars for millions of streams and then receive the silver lining of fair use protection against a label refusing to release one of their albums.