I do agree with the others that Moghedien is a good jump below Nynaeve though ... it's been said in the books (TPoD) that Nynaeve had yet to reach her full strength ... which means months after her battle with Moghedien (when they were equal) she was still getting stronger. It's also possible that Mesaana is equal to Semirhage, but Sandersons comments has me putting a little distance between them.

End of the day for me I think all the Forsaken are pretty damn close in Power ... even Moghedien thinks she has a shot at becoming Nae'bliss which is indicative that she is in the same general range of the others, even if she's the weakest.

If Moggy is weaker than Nyneave - I think its only slightly - almost negligble.

However i agree that on the super power level - it makes little or no difference of raw strength. I also agree Moggy could probabaly be Nae'bliss. You must remember Moggy's defeats are not due to her lack in power or relative weakness compared to the other forsaken - but her defeats are down to her personal traits. She lacks bravery, she lacks perseverance (in fight) and is weaker willed. She is a coward who prefers the easier option. However also please note that the only time Nyneave actually defeated her was in Tanchio - the other times Nyneave was lucky - and saved by sheer fluke at the last minute.

back to strength - If - lets say - even if Graendal/Semi/Messy were on Moggy's level of strength - I doubt the other forsaken would have been so dismissive of them - Granny would have still challenged Sammeal and Lanfear (and tried to bait Messy - like she did in one meeting - where she alluded to Messys desire to be a scholar)- and the forasken she would have challenged would have been weary - because Granny is pyschologically stronger than Moggy - and same with Messy and Semi.

Moggy is just pyschologically weak - even an average Aes sedai is pyschologically stronger than Moggy- Siuan sanche would fry Moggy if she was on Egwene's level or Cadusune's level of strength - however the raw power balance between Moggy and normal Aes Sedai is so unequal - that Moggy would just overwhelm them.

Finally remember how Moggy dealt with Liandrin - she was weak and wounded yet dismissed her in seconds - although Liandrin mounted a surprise attack.

Moggy was confident enough to appear and challenge six or however many they were - black ajah sisters. If you remember she offered them all to test their strength against her! She cowered them all.
Liandrin knew how strong Nyneave was - even though she hadn't reached her potential - Liandrin would have known how strong Nyneave could potentially be - as women can sense the potential strength and would have made a mental note of comparison between Nyneave and MOGGY and told the others how Moggy was less than Nyneave?

I put the Choden kal users at the Strong level (Moiraine, Lelaine, Siaune, Elaida, Romanda)

Meilyn/Karene at the very strong

cadusane at exceptionally strong - strongest of the weakest.

Bode at super strong - the weakest of the super strong.

Elayne/Avi/Eggy at the super strong

Moggy onwards at freaky strong!!! Simply beacuse Egwene seems to believe the forsaken can easily overwhelm her. From the way Granny and the other forsaken carry themselves - it seems she cares not how strong someone is - as she is stong enough not to be overwhelmed. for that matter you may recall Asmo challenges lanfear and is livid at her - and certainly does not act scared of her. Also in one of the aerlier bookes Asmo and and another male forsaken have a huge bust up in the world of dreams - but both shut up when Ishy turns up. i think its in book 2.

Its only Moggy who acts a little cautious infront of the other forsaken - but actually - even she is not cowered by their strength completley - when she meets Moridin - she can see he has use of the True power (so obviously he can channel - and if the Great Lord is bestowing his favours on him - Moggy would know he was a strong channler)and is still arrogant towards him until he pulls out her mindtrap. She is also dismissive of Cyndane - and is not duly concerned abt her superior strength.