Well, ST cards make up in their art for the lack of power/usefulness. They are all brilliant addition for the deckbuider where we can see and admire the art and animation without needing to play them.
Sorceress: One damage will make her useless. You must bring plenty of "boost an ally" card for her to be useful or she is neutralised. Weak and high risk card.
Whisperer: Seems good. 3 damage can kill it, but if not, it can be a +3/turn for a few turns and can easily play for 12+ points in a long round. Comparable to the 4P SY/MO card with a different condition.
Vanadain: Junkest and crappiest card in this expansion or in the whole game for the provision and the ability (at least until Waylay is reworked).
Francesca: A decent card, but needs a lot of planning (other faction Legendaries with the exception of NG) doesn't have hard condition/planning needed to get good value. Can easily brick in a short round (please don't say you can play with MF to get +1 special card. She has no place in MF and to play her in MF to be useful directly means she is horrible). To be able to play 3 special cards is easy in a long round, but in a short to mid round it is very very hard. She will have her place, but once a meta deck with her becomes famous people will know how to smoke her out and let her play for 7 points for 10p.
Overall, the ST package along with the (non-existant) balance for ST is the weakest/junkest and biggest snub for any faction in this expansion.