This is the basic misconception behind the Anubis design. In an anti-spam system, there's a user/abuser reward asymmetry. Users make single requests and get some constant reward V. Abusers make millions of requests and also get some constant reward V. Proof-of-work exploits the asymmetry: costs are, by a factor of ~millions, disproportionately imposed on abusers.

That's exactly not what happens with scrapers. Scrapers make millions of requests, yes. But each one of those requests produces an average (token-denominated) reward V'. There's no asymmetry at all: you're just adding a fixed cost to each reward, for both users and abusers.

That's before you even get to questions like "does the system actually work, or does a single solve get practically unbounded rewards".

no, a single solve returns a token which entitles the scraper to access the site as much as it wants for one week.

not if its running on someone else's device