They won't take it down if they have both an onion site and a clearnet site. The worst that could happen is that they eventually manage to take the clearnet site down (which at this rate, they won't be able to do). In which case, they will just have the onion site, just like you say they should.

I think gatekeeping information is bad. Both behind a copyright, DMCA and DRM, but also by making it more complicated to access or hiding it. Of course, the intention isn't the same, but the result often is.

Piracy is not just the act of pirating, it's also the belief that data should be free, that culture should be accessible to those who can't afford to pay for it, and that by freeing the information, we will make the world a better place. Anna's archive follows that philosophy, and that's why they did the Spotify thing. It's also why they always try to keep a clearnet site, so less technically inclined people have access to all that information.

What copyright trolls want isn't just to eliminate piracy. Making it harder is also a partial win for them.