Well, can we hope it a conversion from metric to standard that's making it look so bad?
Despite what could potentially lead me to abandon playing and sell all my GW if things are as they seem, I can see troops not diving in price for a few reasons. They are the game winning items, so GW seems to price them a little higher than they might for just their gear. I think taking pricing from the standpoint of gear/stats alone doesn't address the game currency exchange inside the mechanics of the win condition.
12 points does sound awfully high for a basic sister, especially when so many limitations are placed on them, like min unit size, etc. However, I think that opinion is based more from my inability to properly use the unit than much else. For me, it's easy to see how to use some units in the game, but troops, especially sisters, have always been too weak to use like the more specialized units, and too many points to risk. It creates a mental block for me that makes me lose games.
My new, masterfully crafted, epic scope plan is to field a ton of troops. Shocking, I know. I'm going to have some specialists, for sure, but I'm looking to see if I can win with 'all' troops, instead.
So, 12 points isn't too bad. It's also harder and harder to shave points the farther down you go. Each point becomes more and more valuable as the model cost approaches proverbial '0'. If the game designer wants a model to cost a point or two less at 50 points, it isn't likely to unbalance the game much, but if he shaves that point on a 10 point model, he's just given the player a 10% increase in resources. Additionally, when it comes to commonly used units, especially 'forced to take' units like Troops, a reduction in 1 point would give you basically two more models, a 10%+ increase in forces. That's probably how they weighted it, looking at larger scales. If they really got fancy, they could point cost it based on total army size or %'s. For example, we all know one Exorcist is ok, but 3 is better, so why not make each one slightly more expensive to put in? I'm not suggesting we go and make it all not fun and what not, but small point size games do suffer from a higher per capita % impact.