Graendal says she did not need her angreal, and added the strength of it just because she could. And Lanfear was weakened, but still stronger than Graednal, and was already embracing saidar. She also had Moghedien with her, similarly prepared, and Graendal was quick enough and accurate enough that she was able to defeat both of them.
And the mindtrap? In what way does it affect channeling?


Graendal was on the verge of being attacked by Lanfear? I see where your ideas about the strength levels of the Forsaken come from, given that you seem to alter scenes in the books to fit your theories.
But fact is that Graendal was the one who got pissed off and made a threatening move against Lanfear. Do you see Aginor or Moghedien daring to do the same? Graendal was the one who coolly baited three male forsaken (one of them Demandred) about the DO wondering if they were still loyal.

As for Rahvin, all she's saying is that if Rand could defeat Rahvin, he cannot be written off as merely lucky, because, as Graendal knew perfectly well, Rahvin was prepared for Rand. If those formidable defenses cannot stop Rand, he isn't going to be a piece of cake to handle, so Graendal intends to avoid conflict.

The truest assessment of her deadliness comes from Ishamael. When faced with an impending duel between Sammael and her, he says there is no way to know how things would go. This when she hadn't even masked her ability, while she herself couldn't possibly detect what Sammael was doing.

As Rahvin said, Sammael was as strong as him. Given what RJ said about the top Forsaken, Sammael was definitely more skilled and mabe even stronger than Rahvin. If Graendal vs. Sammael is difficult to predict, Graendal vs. Rahvin is much more straightforward.

And because one level exists between Graendal and Lanfear's strengths doesn't mean it had any significance when they meet in a duel. One Power duels are not pre-determined on the basis of strength alone. There are many other factors, and from all we've seen, Graendal can threaten Lanfear any day, and the result cannot be predicted.