Surely I don't need to explain how headless browsers work, bot proxies and distributed crawlers to you do I? If you haven't experienced this first-hand, I can understand. Maybe it warrants a blog post. But I can assure you, these don't work at scale, they might only stop the "less sophisticated" bots and maybe (just maybe) some unwanted spam.
What do the browsers being headless or the traffic proxied have to do with anything? Each client still has to solve a PoW challenge regardless. That mitigates the (possibly unintentional) DoS by making it exorbitantly expensive.