Agreed. Skill also makes a big difference if someone who is completely inept is against an expert (Alivia, not knowing about inverted weaves, would be like this vs. Lanfear).

Plus, as you said, we don't know how much willpower or luck came into it. Cyndane/Lanfear certainly wanted her chance to get at Rand/LTT more than anyone than perhaps Demandred, but unlike Demandred she is mindtrapped, so the Cleansing was her only chance to both obey her orders and strike at LTT. So I think that anger and passion certainly played a role there, whereas the others would have held something back.

Out of interest, would it be possible that Cyndane used the TP in that fight? If not, I'm kind of surprised that Moridin didn't attack, with the TP he could have easily ended that battle (though I suspect that killing Rand or Nynaeve during the Cleansing would have detonated the weaves in a Nuclear fashion. So he sent in the expendables).