Say a hash challenge gets widely adopted, and scraping becomes more costly, maybe even requires GPUs. This is great, you can declare victory.

But what if after a while the scraping companies, with more resources than real users, are better able to solve the hash?

Crypto appeals here because you could make the scrapers cover the cost of serving their page.

Ofc if you’re leery of crypto you could try to find something else for bots to do. xkcd 810 for example. Or folding at home or something. But something to make the bot traffic productive, because if it’s just a hardware capability check maybe the scrapers get better hardware than the real users. Or not, no clue idk

This is an aspect that a lot of PoW haters miss. While PoW is a waste, there are long term economic incentives to minimize it to either being a side-effect of something actually useful, or using energy that would go to waste anyway, making it's overall effect gravitate toward neutral.

Unfortunately such a second order effects are hard to explain to most people.