there is no direct comparison in the books that tell us how close Moiraine is in actual strength to any of the Forsaken. All we really know is that she is in a relatively rare strength category for women, and from the recent quote about Pevara we now know Moiraine would be considered strong even among men. We can extrapolate that Moiraine is a little more than 50% as strong as Egwene and that Egwene is well over 50% of Lanfear, but that's about as close as we can really get to a comparison between Moiraine and Lanfear without a direct quote.

Training (or lack thereof) will create an illusion of even greater strength for the Forsaken as they can do many things modern AS have no clue are possible. Many of these things don't rely on strength, but have spectacular effects ... Compulsion clearly doesn't require vast strength as Delana can do it just fine, but it does require specialized training and arguably has a more potent effect than things that require a lot of power like the invisibility trick Elayne has to create ter'angreal for because most AS don't have the strength for, yet it's practically a useless weave! It would be easy to assume the more powerful individual is the person who can use Compulsion, when in fact the opposite may be true.

All of the Forsaken are capable of many things that make them appear even more powerful than they are ... Lanfear's ability partial shield on Asmodean was clearly a matter of her superior skill in this area, not simply raw power. She even notes that he could have broken free if he was willing to push his limits. IMO it's unlikely that Lanfear is actually stronger than Asmodean, but she is clearly more effective.