>it's that you cannot bypass it at scale.

Define "scale". For any reasonable wait that you're willing to impose on your users, any PoW scheme heavily favors attackers. They have unlimited time and can be scraping even while they're asleep. Your visitors on the other hand don't have that luxury. You might argue that's not the point and it's only to stop dumb scrapers that are effectively ddosing your site, but if it's just dumb scrapers, you could've stopped them less onerous measures like tls or javascript fingerprinting.