> Bots want to open many orders of magnitude more pages than a normal user, so the resource investment for each single page matters a lot more to them

Depending on the configuration, Anubis will supply a token after the challenge that bypasses the challenge for a time.

So any scraper that retains basic cookies will be able to bypass the challenge for a number of page views.

A user who needs to load a single page and a bot that wants to scrape a number of pages may pay the same cost.

The amortized per-view cost is highest for the real user.

Now you have a session of sorts and can limit the requests for that client, right? They can be fast, just limited in volume - regular user isn't punished.