Ignoring the other criticisms because they generally seem valid, to everyone saying that proof of work doesn't matter because bots can just use more machines, that depends a lot on the economics of any specific automation project. I scrape a little data here and there, and a reliable proof of work system costing ~20s on a commodity core would make some of my personal projects cost tens of thousands of dollars monthly. Maybe that's worth it to someone (e.g. if they have an army of hacked machines without anything better to do), but I think it'd keep a lot of the riffraff out.