Storms Sorceress is 4 points and adds this as a special action to the unit that she is added to:
"Roll 1 blue die. For each surge, choose and enemy at range 1-3. Each chosen enemy suffers [RED RUNE] damage."
Compare that to the 6 point Uncontrolled Geomancer:
It seems like the Geomancer will really take some work to get into situations where its worth using his special while the Sorceress is is going to find a lot of opportunities to toss out some damage with her special.
The only thing that I can think of that makes the prices make sense in comparing these units it that there's a decent chance that special action from the Storms Sorceress may end up doing nothing if depending on the dice roll.