I'm not making an argument about the strength gap. The Forsaken are also among the most skilled Channelers who ever lived. Coupled with being among the strongest channelers who ever lived means if you are weaker than they are you must be MORE skilled than they are in order to stand a chance. Egwene level is clearly a step lower than Forsaken, thus for someone of that level to compete with an individual such as Graendal or Demandred they would need to be supremely skilled or they would get destroyed pretty quickly. It's akin to a boxing match where you are already giving up size and reach to you opponent, if you also give up skill you are heading for pain.

Moghedien and Asmodean showed a shocking lack of skill, but that may not be too surprising if you consider one was essentially an investment banker and the other a musician. Not exactly trained for dueling and the odds of them having to face off against an equal or greater force in their own Age would have been slim. And neither of them initiated the duels so they started off on the defensive from the beginning.

With that said even someone like Nynaeve who is on par with the Forsaken would need the skill to match them or to truly be a threat. Graendal herself makes note of it in TOM when she decides she must kill Nynaeve if Nynaeve has figured out how to unravel Compulsion ... Suddenly Nynaeve became a skilled opponent and thus a threat. Graendal had just as clearly been keeping tabs on Nynaeve looking for signs of such skills.

Mesaana says much the same of Egwene when she tells Sheriam that Egwene must be removed as Amyrlin. She isn't directly speaking of OP matters, but she acknowledged that Egwene was not what they wanted in the role ... They wanted a girl not a woman. It's a clear indication that the Forsaken do not wish to face off against opponents with any type of skill. This theme has gotten more pronounced throughout the series as the remaining Forsaken have hunkered down into their tasks. They are much more cunning and skillful in their attacks ... Even the ones that fall apart.

And of course Demandred wants the advantage of a sa'angreal ... That's the variable he has the most control over! Why face a possible loss if you can magnify your strength by 10x and not worry about LTTs superior skill ... There is a point when overwhelming strength differential makes any duel a moot point.