Power Tempest (Wildfire)
The Scepter/Warhorn Power Tempest: the same Fire/Air core as the Spear build, on a weapon that also hands the group protection and a pull.
Wildfire keeps the pile burning, which is exactly what 
Persisting Flames and 
Pyromancer's Training pay you for. 
Sand Squall extends the boons the squad already has; 
Cyclone pulls.
Why these traits
The same Fire/Air/Tempest core as the Spear and Staff variants: 
Fresh Air for the repeatable air burst, 
Transcendent Tempest for the overload payoff, 
Power Overwhelming and Persisting Flames for the Fire multipliers. The warhorn is what changes — Wildfire burns, and burning is what Persisting Flames and Pyromancer's Training reward. The two weak majors are the same as on the Spear build: 
Conjurer only fires when an ally picks up a conjured weapon and you carry one conjure, 
Conjure Fiery Greatsword; 
Tempestuous Aria needs a shout or an aura granted to an ally, and this build has neither.
Gear reasoning
Marauder, Berserker's and some Valkyrie with 
Deadeye. The Valkyrie pieces buy vitality and ferocity without precision, which 
Zephyr's Speed and 
Signet of Fire's passive already supply. The sigil that differs from its siblings is 
Frenzy: two seconds of recharge back on every equipped skill when you kill something, where they run 
Impact for burst against stunned targets. 
Fireworks rewards weapon skills with a recharge of 20 seconds or more — Wildfire is 30.
When not to run it
Frenzy and the Valkyrie pieces point the same way: this variant expects to be in the fight for a while rather than landing one window.
If you want the burst package instead, the Spear variant runs Impact and the same traits. And like every Fire/Air Tempest here, this build has no 
Stability and no blink — 
Armor of Earth and 
Lightning Flash are both available, and neither is slotted.