On my first times using turret users I too felt disappointed at the low damage. I started to compare turret damage with other tech powers. Using Paladin or Quarian female engineer with their powers up thinking they would detonate as hard as Biotic detonations. Result: disappointed.
Then I kind of realized that Tech powers like cryo, incinerate, the electrical one, and TURRETS, are not meant for high damage like Biotics, but to weaken or disable enemies with status(burn, freeze, stun).
Turrets have almost as low damage as fire, ice and thunder tech powers, but they shoot many times. And they are usefull for attacking enemies behind covers. Dont count on it as a distraction when running away from many enemies, they often will ignore the turret and go after you. Poor flamer turret, all alone, being ignored by enemies

I think that engineers have to level their weapon damage instead of power(maybe 4B since they may need speed charge up), since fire, ice and thunder will not do lots of damage but weaken enemies defenses.