our understanding is.

a circle of three is nothing compared to a circle of 13.

In regard to the power of the Cleansing circles.

First let's cover that the via Asmodean two average women match up to an average man. So the "actual" strength of that circle is approximately 4 women. Rand in his point of view believes that four AS, possibly linked, but possibly not, aren't a challenge. In fact he seems mostly concerned at 6. So if the total strength of the circle facing Demandred was about 4AS or 2AM if you want to compare to those who faced Sammael then technically they couldn't have been more than a nuisance. Even if Rand's estimation of four AS included the possibility of them linking the mixed gender increase to the circle brings the strength up even further than a regular link. This isn't inconsistent by being too strong or by being too weak. In regard to the increase in strength lower exponents aren't that significantly far from the base number 2^3=8 isn't that far from 2x3=6 but 2x13=26 definitely is a far far cry from 2^13=8192. Unless we can figure out the actual formula for a circle's increase in precision general understanding of exponents is all we can go on. So in my estimation, a three person circle with average channelers should not be drastically stronger than Rand or Demandred. I think because it was a mixed circle that they were even a contender.

Second the men and women at the Cleansing are new at it. You can't expect them to do a great job when its their first time.

Moving on to the 6 AS needed to take down Logain and Rand. First there is the evidence that AS use multiple shields to capture men by Rand's six soft points. And this is supported by Cadsuane's decision to fight the bubble of evil separately instead of linking. In a circle non-channeling members are vulnerable. The benefit of the link would require that linked women be close enough to use that link without getting picked off. And while hunting down a powerful man may benefit from super effective weaves, the AS oaths would also restrict them from the kinds of attacks they could make to get to him. I believe the main reason the folks at the Cleansing linked had more to do with the mixed gender of the Forsaken they'd be fighting than it being the best combat strategy.

So to recap the effectiveness of a three person link is at the bottom of the exponential effect and so expecting the Cleansing circles to decimate the Forsaken is expecting too much. And there is at least some evidence that AS strategy does not include linking during a battle and definitely some evidence that men are multi-shielded not shielded by a circle at least not once captured.