To a point yes, for the crawler bots, but Anubis uses a lot more resources to keep the bots busy than a simple firewall ignoring the request. And if there's no response vs a negative response, the requests are likely to fall off more quickly. And the even more significant load might be from malicious login attempts which use even more resources and Anubis likely won't be as effective on those more targeted attacks depending on the types of services we're talking about. Either way, firewall blocks are way, way less resource intensive than any of that, so as soon as you open up that firewall and start responding to those malicious or abusive requests they will become progressively more resource intensive to mitigate.