What's actually stopping them isn't the PoW, it's the customisation effort. If one site has Anubis nothing scrapes it. If many sites have Anubis they write counter scrapers. Today if you make a slight change to the Anubis algorithm on your site, they'll burn CPU endlessly computing hashes with the original algorithm and submitting wrong ones.

The author of Anubis hates this fact and will ban you if you mention it, so don't. He insists it's the PoW.

sounds right to me. ai will shred it