If Ishamael is superior to the others, I just haven't seen it. The only time he's gained any real advantages has been after Moghedien and Cyndane were mindtrapped and given to him, and that was after he had suffered multiple defeats and been given a new body.

If it came down to an outright fight, and the Dark One commanded them to fight one another to the death using any means necessary, I tend to think Ishamael would be one of the first eliminated - the only thing that seems to keep him from being wiped out is the uneasy amnesty that exists among the Forsaken for most of the series - he shows himself incapable of grasping basic experiences that the others understand very well, most probably because he is partially insane and because of his use of the True Power, probably worse off than many of the male channelers running around insane.

He just never struck me as a legitimate threat in the way Lanfear, Graendal, Sammael, semirhage or Demandred have. Ishamael seems to have suffered the most from the "BS degree in Evil Villainy 101" syndrome.

In fact, I think that there were many Aes Sedai during the Age of Legends who were equal to Lews Therin, all things considered, including Latra Posae Decume - we know Lews Therin's weak points probably better than any channelers at this point, not counting my personal feelings that he is especially attuned to Air, Fire and Spirit with weakness abilities with Water and Earth. He seems to balance quite well with the Forsaken, who were his peers, and channelers of his own comparable potential in terms of capability to channel greater volumes of the Power next to their various skillsets.