I see the results against low T seem to be similar to the BG, one thing to bear in mind though is how much cheaper WE are and it appears they do comparable damage despite the point difference. In your example a unit of 5 BG with TM would be 79 points, while the WE with hag would be 60, basically allowing two more WE for the same price as the BG unit. Now there is no question who would do more damage, the BG dealing 11 while the WE deal 22.
Their champion can take magic items. Once again very big in my eyes because it lets you do things like stick a Ring of Hotek in the center of your line without taking up a master's item points.
Don't forget a hag can take a gift of khaine. I know that may not be as good as a magic item, but it can serve to enhance a WE unit well.
I will agree that BG are much less sensitive than WE, but played right WE can be most dangerous and clearly have one strong edge over BG with poison.