They're supposed to be played with mercs. The trouble is mercs are problematic with certain cards, like BMC, unless you always mulligan every BMC away. I mean, a merc at two means you lose 2 pts to put out a bronze special, which have wildly different values depending on circumstances. Some can be big point swings under ideal conditions (thunderbolt, lacerate, shackles, to name a few). Many are going to be undervalued compared to some bronze units able to better fill the same role (case and point, trapper vs lacerate). In any case it's hard to have solid control over the value on a merc.
Sappers at 7 still seems low. Pulling back mercs makes it a 9-13 pt card, which is moderate to decent compared to other options at first glance. Most dwarves are going to provide better value due to synergy with other dwarves, however. The biggest issue is, again, it's hard to have solid control over Sapper value for a variety of reasons.
Morenn is valid, especially because 5 damage can drop/stop a number of setup cards. But other cards can too, with more control over what you're shutting down. Toruvial can work too. A major drawback to her is having her get locked though.
TBH, I find most ST options are fine to win a round. The issue is they are forced to burn too many cards for their setups to do it, and run out of steam for the other rounds. And, as big of a change as it may be, I think the faction needs cards to interact with it's own graveyard. Say, a rework of healers to work like medic type units. Every other faction can bring back units or mass spawn them, with basic units, except ST. For this reason everyone else can re-setup and re-play important units/combos. ST cannot do so....