Destructive Clench will retain unique effects depending on which staff you use. For Shock Clench, it turns the attack in to an AoE and deals the "AoE damage standard". This standard is that AoE abilities deal 33% less damage than single target abilities, correct?
So Shock Clench will deal 33% less damage than Flame or Frost Clench? That's going to be one hell of a tool tip to explain all that. If the tool tip displays one damage value it would be incorrect.