Is it possible Moghedien is stronger than we imagined, but because she is pretty much a coward, the other Forsaken dismiss her?

I agree with you. I think Moghedien is still the weakest Forsaken. But we could possibly move her up a level or two and still have her at the bottom of the Forsaken, especially if Graendal and Mesaana are on the same level. It could look like this:

Lanfear / Alivia / (unnamed character option 1)
Sharina / Talaan / Someryn (unnamed character option 2)
Semirhage / Nynaeve
Graendal / Mesaana
Cyndane / possibly Moghedien
Moghedien (alternatively goes here if we want a gap between her and Cyndane)

In my list above, I assume there is another character who we haven't met yet. The unnamed person either falls on the Lanfear / Alivia level or on the Sharina / Talaan / Someryn level. Also, Moghedien could be just one level below Graendal and Mesaana. Or Moghedien could be a couple of levels below Graendal and Mesaana. How do we know how far down to put Moghedien?