Morghase used her ability to wave a handkercief for a long stretch of time to attract attention to the building in which she was trapped with Faile and co. That's a great deal more than Egwene could do with dosed with Forkroot (she says she could swat a fly and it wouldn't feel it).
Sorelia may have been just as strong as Morghase, but better trained. The Tower didn't bother because it thought Morghase's ability was useless. Sorelia learned, allowing her to be part of circles reliably, and thus a part of the Last Battle. Its a true testament to the utter uselessness of Tower training for those they considered too weak.
I'd call Egwene's statement hyperbole, and there is the fact that she could also create many balls of light and split her flows and consistently reach the Source despite the forkroot.
Morgase spent hours focused on moving that scarf for seconds at a time and didn't manage it with any kind of consistency. Sorilea is clearly stronger than Morgase, if still incredibly weak. When she needs to reach the Source it's there for her and she can manage at least forming weaves with no difficulty, something Morgase is incapable of. Training certainly plays some role in that, but given that the WOs don't focus nearly as much on OP training I doubt Sorilea is much better with saidar than an average AS or even Accepted ... given her extreme weakness in the Power it's not like she would have spent all that much time training it
