> Don't the bots still need to do the proof of work for Anubis? They can't "async" their way out of that work.

The implication is that while they are waiting for the async loop to complete for one site, the bot can be scraping others that have already had the challenge completed (usually the one challenge stays in force for some time afterwards) or that have no such challenge.

Memory hard challenges will reduce the effectiveness of this, but not remove it completely.

Though that these methods are working at all implies that most (almost all?) bots are not bothering to use such async methods as there are sufficient resources not protected by them that this complication is not yet worth implementing.