I tend to see Cadsuane as the "middle ground" you refer to and Egwene yet another rung up from that ... IMO Cadsuane is 2x an average AS (say Verin), Egwene 2x a strong AS (Sheriam) and Nynaeve 2x a Very Strong AS (Moiraine) ... the proof is in the books that Cadsuane is a long step above all other AS and there are at least strong hints that there is a long step up to Egwene given that Bode is likely stronger than Cadsuane but still weaker than Egwene, and Nicola may well have also been between Cadsuane and Egwene.

Egwene was about Moiraine's level at the start of TSR (maybe a bit stronger from her comments to Rand), but Elayne was significantly below her at this point ...

TSR
Into the Palace

Egeanin, arms folded in front of the doors, seemed ready to let it go on, but Elayne wove flows of Air around Amathera's waist. To her surprise she was able to lift her off the already senseless woman and set her on her feet. Perhaps learning how to handle those heavy weavings from Jorin had increased her strength.

We know from Siuan's later comments that she was once strong enough to lift about 3x her own body weight and here we have Elayne being surprised at being able to lift a single woman and noting that her strength must have grown between the Rand encounter and this moment at the tail end of TSR.

Rand essentially overwhelmed a Moiraine level woman and a woman likely not much above average AS strength ... maybe Verin strength at most. This is not a surprise since not much later we see Verin and Alanna linked even less effective against Rand!

I think people often forget that Egwene has been pretty far ahead of Elayne in strength for most of the series. It's clear that Elayne was maybe 50-60% of Egwene in current strength when they encountered Rand. And Egwene was probably at about 60% of her maximum in this encounter.

The real problem I see in the consistency is how strong AS really are ... there is a wide range of quotes that contradict where AS strength stands. I agree that the average women are very much weaker than FS level, but the Strongest seem to be closer to 50% of that level. And IIRC Brandon has come out and said the strength range of AS is much larger than we all seem to think... which is logical given Siuan was about 3x Daigian, and Daigian would fall right around the lowest end of average female strength on a Bell Curve.

I also think there is plenty of evidence showing that Nynaeve and all of the Forsaken basically make up about the top 10% (or so) of the strength curve with Egwene and co in the next rung and then Cadsuane/Bode/Nicola the next ... after that you get into the "average level women" that probably peaks around Moraine and ends at Daigian before you hit the truly weak women such as Alise etc ...