How can you use the dexterity advantage in Lanfear's case, but not in Egwene's circle's case. They are both examples of females matching males. Therefore, the Egwene, Romanda and Lelaine circle ALSO have the female dexterity advantage over a male Forsaken. So in other words, if Lanfear is able to match a male Forsaken thanks to the female dexterity advantage, and if Egwene, Lelaine and Romanda can match a male Forsaken thanks to the female dexterity advantage, then it means Lanfear must be able to match Egwene, Lelaine and Romanda. And since the female dexterity advantage plays no role when females face females, it means that in RAW STRENGTH, Lanfear must equal Egwene plus Lelaine plus Romanda.

It's like reading in the text that Mike Tyson is as strong as Arnold Swarzenegger, and reading somewhere else that Hulk Hogan is also as strong as Arnold Swarzenegger, and therefore, you can deduce that Mike Tyson and Hulk Hogan must be of similar strength.

Since Egwene's circle can match a male Forsaken, and Lanfear can match a male Forsaken, it means Egwene's circle and Lanfear must be of similar strength. The dexterity advantage is needed in both Lanfear and Egwene's circle's instances in order to match a male Forsaken. And therefore, when they face each other the dexterity advantage is neutralized and their raw comparative strength must be similar.

As for Semirhage's shield being held by 3 Aes Sedai, it is clearly stated in the books that you don't have to be as strong as someone to hold a shield on them once they are cut off from the source. You can in fact be much weaker and still hold a shield quite comfortably. So the fact that 3 Aes Sedai hold Semirhage means that she is probably as strong as 4 or 5 of them linked if she is already holding the source.

In the same way, the 2 Black Ajah sisters are able to hold a Shield over Nynaeve in CoS despite the fact that they are not close to her strength, even if they are linked. Remember they are two average strength Aes Sedai at best. And yet, Egwene is stronger than two very strong Aes Sedai. And in turn, Nynaeve is much stronger than Egwene. So there is no way that two Black sisters can match Nynaeve. Yet if they shield her before she holds the Power, they can maintain the shield despite being much weaker than her. In the same way, Rand can be held shielded by far fewer women than it takes to cut him off from the Source in the first place.

Lastly, the weight comparison is based on complete guesswork. Rand is 6 foot 6 inches tall according to RJ. And Lan isn't much smaller than him. How big is a Sea Folk Windfinder? We don't know. So that is certainly not good evidence of anything. Plus we don't know what the physical limits on lifting weight with Air is. It may well be limited in the same way that building a bridge of Air is limited.

In any case, I think the above makes it clear that Lanfear HAS to be as strong as Egwene plus Lelaine plus Romanda, if she can match a male Forsaken in the same way that Egwene's circle can.