which also leads me to believe RJ didn't really have a "scale" for dexterity and there's nothing to say it was a constant additive bonus for women (realistically this would mean there was only one scale for both men and women and totally negates the point of the ++ levels).

I personally don't care all that much about the "effectiveness" scale since it's clear that RJ didn't create one and didn't seem to really think about something like this beyond a few passing comments, he certainly never gave us enough information about two channelers to conclusively say "X was more effective than Y". We see no clear effectiveness difference between any of the Forsaken really, Graendal is weaker than all but Moghedien, yet had no problem believing she could kill Sammael a ++2 man, who in theory she would be less effective than.

The whole effectiveness conversation seems to only matter for the purposes of trying to back into an actual strength level for certain characters IMO. And I certainly don't think there is enough information to say there is a direct correlation to a ++3 man and a 3 woman or that a level 13 man could only be as effective as a level 19 woman and so forth ... at least not off of the information that they could both create a useable gateway. This can too easily be explained by superior Talent or stronger flow affinity, especially since we've seen channelers perform feats that should be impossible due to a Talent or a flow affinity. Weaves and what could be done by a man and a woman sometimes just varied. We know men and women have different weaves for Traveling and only one strength minimum is mentioned, perhaps the way men Traveled was just generally easier than the way women did it. We know air bridges have a maximum distance they could span and that a weaker woman could achieve the same as Rand could etc...

I think RJ wrote what fit the needs of the story and explained it with whatever device he deemed necessary. Beyond him making the general remark that women are more dexterous than men, I don't recall him ever giving a single detail about dexterity. He typically used Talent or flow affinity as his rationale for someone being particularly good at something.

Egwene's Earth affinity = cuendillar, other women with good strength in Earth could do it better than much stronger women

Siuan could still Heal to the same ability after her strength reduction

Ashmanaille could Travel, but didn't have the requisite strength to even make a non-useable gateway

Androl could make gateways well beyond what any of the most powerful channelers could achieve

Berowyn and her Shielding

Thing is, we have almost nothing to compare a male and a female channeler's strength. The only reason we even think they are different is because RJ said so, the OP feats in the books themselves give us no indication that Lanfear or Semirhage were as effective as Ishamael or that Mesaana was the same as Demandred or Aginor.