A better, perhaps the best, argument is that a worse bot mix might appear tomorrow, so anubis should be used as a runway for a better solution, and not as a solution in itself. If only everyone with a website had the desire (or AI tokens) to implement their own better solution. In some cases even desire or a lot of tokens isn't enough. I mean, you think kernel.org folks haven't put some serious thought into it? And yet, as HN argues about it, there's kernel.org running anubis at difficulty 5.