Having converted to audio books, rather than physical books these days for WoT, quite hard to find specific scenes anymore, but from my recollection:

Regarding the helpless Sul'dam, my recollection is that Egwene freed the Damane, and then after that killed the Sul'dam, who realistically at that point weren't a direct threat, and I think it is debatable that a sister who had sworn the three oaths would have been able to kill them.

My recollection of Egwene's death is even shakier, as can't recall all the intricacies of it, but it wasn't that clear to me that she needed to overdraw in order to wipe out the Shanaran channelers - it seemed that at that point she gave up somewhat, following Gawyn's death, and so let go of things, and may have got almost the same impact either way.