So here's what I'm thinking -
Since this is a game about going on crusade, I'm going to assume fanaticism is going to be appropriate. Which means some warhammer level of purging.
So, with that in mind :
Champion of the Faith archetype,
Deity : Asmodeus (for the mace, also edgy devil boi)
Spec into Hellknight Signifier, join Order of the Godclaw
Take Aeon Path, then Devil path
Commit war crimes along the way.
That should make a sufficiently edgy boi whilst still being somewhat logical thematically.
I wanted to go Zon Kuthon but Godclaw doesn't cover him and if I'm playing a crusading fanatical warrior priest I might as well go Godclaw.
I like your game plan in theory.
Although personally I'd hesitate before nerfing my character by going on an inferior late-game path.
Like Cyberarmy wrote, Aeon itself can be very much a "Judge Dread" type character. And late game Aeon is insanely strong (though it starts slow).
For Aeon - and particularly non-inquistitor Aeon - I recommend installing TableTop Tweaks mod - including the Mythic Reworks module. Otherwise the Aeon Bane is a very limited resource for non-inquisitors.
Mechanics-wise, Warpriest is one of the classes that really reward staying (mostly) pure.
Your weapon damage, Smite damage, Blessing effects all scale based on class levels.
So going for HK Signifier would be a purely RP choice, resulting in a weaker character overall.
There's a mod that adds the missing Catechesis Signifier class feature - that could at least allow to continue progressing Domains on an inquisitor / cleric or Mysteries on an Oracle. But I doubt it works for Warpriest Blessings, much less CotF Smite.
Although now that I think about it, there is a bit of anti-synergy with your class and path choice. Both Aeon and Warpriest invividually have crowded Swift Action economy (Aeon Bane, Swift Action regular and Aeon Mythic Spells, Fervor Swift Action Spells, Swift Blessings, Smite). Adding the 2 together means you will be unable to use half of your best features in most fights (and by the time your battle-ready, most battles will be mostly over).
Also, it may not be a huge issue, but there will be a large overlap between your class and Mythic Path spellbooks. Although spells from Mythic spellbook will be gained much later and will scale much slower.
As much as it pains me to write this, as I love BOTH your class and path choice, I recommend that you either change the class - maybe to a Judgement-less inquisitor (to avoid overcrowding Swift Actions) - like a Sanctified Slayer OR the Mythic Path (lich would have a different vibe - and to realize its full potential you should be a full arcane caster and merge the spellbooks for hyper-speed spell and Caster Level progression - but its definately not lacking).
Alternatively do some martial Godclaw Hellknight character, obligatory with Fearsomeness Discipline to make the enemies scared shitless when you engage them.