You can't be serious, can you? Explosive Dart costs 16 Heat, which takes 3.2 seconds of recovery time to dissipate. In exchange it does AoE damage to up to 3 enemies. Compare that to Smash. Smash costs 3 rage which takes 2.75 seconds of recovery time (Assault) to generate. In exchange it does AoE damage to up to 5 enemies. And the damage is about 3-4x greater than Explosive Dart. In what imaginary world would the Merc's AoE be considered a "decent bang for the buck"?
You did it wrong again.