When Egwene thinks that she+Romanda+Lelaine might match 1 male Forsaken, she of course does not base this on the male's actual strength, but on his effective strength.

Because she cannot sense a male's actual strength. All she can judge it on is his effective strength, such as Rand demonstrated when she and Elayne were treated like "kittens by a mastiff" when trying to teach him in the Stone of Tear.

The point is, she doesn't mean that she and R+L can match the RAW strength of a male Forsaken, as she has no idea how to even measure that raw strength.

What she seeks to match is what he can effectively DO with that power. Meaning his effective strength. Thus, she is not comparing Her, Romanda and Lelaine to a strength level several levels above Lanfear.

Instead, the comparison is to Lanfear's effective strength level, which is the same as a strong Male Forsaken's effective strength level.

Simple really, once you apply logic instead of wishful thinking.