If equal strength women can shield one another based on skill then it is not necessary to be MUCH stronger than someone in order to shield them.

I think what you are getting at is what Sidious is talking about.

Egwene is 2x Sheriam, and in TGS slaps a shield over her, cutting her from the source without breaking a sweat, she is both overwhelmingly stronger and more skillful/deft than Sheriam. Thus she "smothered" her.

On the other hand Nynaeve failed to Shield Elayne despite a goodly strength difference, obviously because her shield was not woven deftly enough, but it also shows that Nynaeve is not enough stronger than Elayne to "smother". In this case Nynaeve needed to either be even stronger than Elayne than she was, or weave a far more deft shield to cut Elayne off from the source.

Later, Nynaeve is able to shield (and them become shielded) by an equally strong channeler. Meaning the shields in question had the necessary deftness to perform the task.

What this means is that Lanfear was able to weave a shield with sufficient deftness and strength to in fact cut Rand from the source, but he was skilled enough to defend himself and thus avoid being cut off (if only just). I agree that in all likelihood at full Strength Lanfear would be unable to shield Rand, but it would be close IMO as Rand was already at least as strong as an average strength male Forsaken. 2 Forsaken would easily smother Rand.