The Greatest powers on Middle Earth (3rd age)... Listed in order

[Voralphion]

and the Witch King would have to go after Galadriel, for the very good reason pointed out by Chancellen: no male could defeat him.

It doesn't say that no male could defeat him, but that none would. I think the quote is "His doom lies far off, and not by the hand of man shall he fall."
This doesn't mean he couldn't be killed by a man but that he wouldn't, he was killed by Merry, a hobbit not a man.
Also if you take more power as the ability to defeat someone in battle, then Merry would have to be higher than the Witch king and Gil Galad would have to be higher than Sauron.
This is not the case so you can't put Galadriel higher for that reason.

[ March 10, 2003: Message edited by: Voralphion ]