I never said the approach was so stupid it could never work. I just shared how it’s annoying and how I worked around my annoyance.

An even stupider approach would work exactly as well or better, like a form saying “type the letter y in this box to continue”. The only benefit is as a road bump that makes the site in any way custom. The moment anyone you are defending against so much as looks at the mechanics of solving the challenge it completely falls apart.

A significant amount of the effect is everything outside the proof of work. Not the cost of hashing but the need to run the javascript that submits it.

If you've seen anyone post a comparison of crawl rate versus difficulty, I'd love to see it. There's probably some difference but I want to know how much of the overall effect it is.