The premise here is fairly simple: the Battle Harbinger is meant to be a divine class who can fight well in martial combat and deploy auras. As it so happens, there's a divine martial class in Pathfinder that already comes pre-packaged with an aura and even spell proficiency progression, specifically the Champion. The latter class even comes with causes and tenets that spur them to action, much like a battle creed, and they can even take up oaths to combat specific foes! Thus, with just a few feats, I think the Champion could be easily made to fit the Battle Harbinger's niche much better than the Battle Harbinger themselves. Here are my suggestions, with a TL;DR below:
Traits: champion
Prerequisites: champion's aura
You can allow your deity's power to radiate from you, bathing creatures in your aura with divine energies. You gain a devotion spell based on your deity's divine font: beatifying aura if your deity allows heal, or execrative aura if your deity allows harm.
Traits: uncommon, champion, concentrate, focus
Duration: sustained up to 1 minute
You bask in your deity's glory, spurring creatures within your aura to fight with renewed zeal. You and allies within your champion's aura gain a +1 status bonus to attack rolls, damage rolls, or saving throws, which you choose when you Cast the Spell. Once per round on subsequent turns, you can change the effect to a different option when you Sustain the spell. Beatifying aura can counteract execrative aura.
Traits: uncommon, champion, concentrate, focus
Defense: Will; Duration: sustained up to 1 minute
You exude your deity's hatred for its enemies, impeding foes who dare to exist in your presence. Enemies within your champion's aura must succeed at a Will save or take a -1 status penalty to attack rolls, damage rolls, or saving throws, which you choose when you Cast the Spell. Once per round on subsequent turns, you can change the effect to a different option and force enemies in the area that weren't yet affected to attempt another saving throw when you Sustain the spell. Execrative aura can counteract beatifying aura.
Traits: champion
Prerequisites: Aura of Devotion
Trigger: You deal damage to a creature with a successful Strike, and your beatifying aura or execrative aura is active.
As your blow lands true, your triumph reverberates across your divinely-suffused aura and renews it. You Sustain the triggering aura.
Traits: champion
Prerequisites: Aura of Devotion
You reaffirm your commitment to your deity's cause with even greater fervor, channelling even more of your deity's glory or hatred. When you Cast beatifying aura or execrative aura, and each time you change the aura's effect, you can choose two options instead of one.
Traits: champion
Prerequisites: Radiate Exultation
Your greatest triumphs against your foes saturate your aura with even more intense deific power. When you Radiate Exultation and critically succeeded on the triggering Strike, increase the triggering aura's status bonus or penalty by 1, to a maximum of 4. This value remains for the rest of the aura's duration.
Traits: champion
Prerequisites: Redoubled Devotion
Your commitment to your cause is unquestionable, and your deity grants you unlimited sanction when you channel their power into your aura. When you Cast beatifying aura or execrative aura, and each time you change the aura's effect, you can choose three options instead of two, and can choose from all the options listed in both spells. Choosing to impose a penalty causes enemies not yet affected by your aura to make a Will save, even if your spell wouldn't normally induce a save.
Traits: champion
Prerequisites: Aura of Devotion
Trigger: You roll initiative.
Your aura of devotion is like a battle cry from your deity itself, surging from you at the first sign of combat. You Cast beatifying aura or execrative aura.
Traits: champion
Prerequisites: Master Cleric Spellcasting
Your closeness to your deity has made them choose you as a representative of their faith, granting you even greater magic that can be changed in preparation for warfare. You gain a 9th-rank spell slot from Master Cleric Spellcasting, in addition to the spell slots it normally provides you.
Each time you make your daily preparations, you can choose to prepare for war. If you do so, you lose all of the spell slots you gain from cleric archetype feats of 7th rank and below, and gain an additional 9th-rank spell slot from Master Cleric Spellcasting. If you have the Divine Breadth feat, you also gain an additional 8th-rank spell slot from Master Cleric Spellcasting. These spell slots last until the next time you make your daily preparations.
TL;DR: With just a few feats, you could easily have the Champion use their aura to buff or debuff to an even greater extent than they do now, and so more smoothly than with a Battle Harbinger. In fact, with just one capstone feat that would reward a 5-feat commitment to a Cleric archetype, you could even go full Battle Harbinger with wave casting!