I don't think PoW scales, because if the bot authors get serious they'll start using native implementations that are much more efficient than the web ones real users are running. In theory maybe Anubis could start using WebGPU to help close that gap, but then anyone without WebGPU support is out of luck.

Then again, a large portion of the problem seems to be bots making way too many requests and in general not being optimized in the first place, and this does help filter those out.