We're are talking about PDFs. A few mb usually. The speed hit of tor is probably fine. Also its a text book. Most users probably find some download latency acceptable.

I imagine the real reason is normies dont have tor installed.

Not a fan of the term “normies” but as a Tor “normie” isn’t Tor traffic identifiable and wouldn’t using it make it easier for authorities to focus on you?

Yes, but in most western juridsictions using tor is acceptable so that is fine.

There are ways to disguise traffic (onfuscated bridges) but those are always going to be an arms race.

You only need a dynamic-DNS system on the hidden service. Then you can avoid the regulatory capture of registrars and host in a friendly country.

For now. Right now DNS blocking is used because it works for 95% of people. Once it doesn't, they'll start demanding more serious means of blocking.

I'm surprised that didn't happen yet because DNS blocking is so ineffective. It's basically just akin to removing a business from the phone book or yellow pages.

AA is purely an indexer, the performance hit would be more felt during the actual downloads.