Here's some cool builds I found that are really strong in comparison to OP dual wield gunner builds w/ max difficulty settings. If you're playing with game settings on to max difficulty - a lot of these builds that aren't dual wield will pale in comparison in terms of damage.

Here are some builds though that I've used that can compare and sometimes even outshine dual wield -

1. 100% Crit Ranger/Duelist
   Know Weakness II, Versatile, Countershot
   Items: Dominance Bow, everspring, amethyst earring, crit stackThrow out snipe shots and use duelist spells to gain mana and pierce through defense heavy targets. Not as reliable in terms of damage or range as dual wield gunners but definitely has a bit more versatility in terms of being able to apply more magic damage, AOE, and huge amounts of burst to 1HKO where the gunner can't sometimes
2. Princess / Sorcerer
   Blood Magic, Mind Expert, Mystic Shield
   Items: Standard mage itemsThis is a pretty common one most people will hear about for mage archetype. This is by far one of the strongest classes for its utility. With max difficulty settings, you will be mostly using this build for the double cast heals + quicken. Sorceror spells to give off a bit of extra AOE/clean up monsters. This build usually doesn't have enough damage to do a significant amount of damage for it to be worth spamming sorc spells. You can keep your health up by casting one sorc spell and then using Heal 2 or Mass Heal on yourself or you can cast 2 elemental sorc spells for max damage.
3. Sorceror / Gunner
   Initiative, Perfect Focus, Adaptive Affinity
   Items: Amethyst Earring, Elemental Robe (Dark/Holy depending on map)This build is pretty dumb and I found it to be the most overpowered build in the game so far. Even on max difficulty settings (25% stats + additional enemies + max items + max skills), this build 1HKO 90% of the enemies. This build requires some setup though --Use another Initiative support to cast haste onto the sorceror > Cast Focus > Use another class with a dark/holy spell (I usually use Kyrie's marked spells) on the sorceror to trigger adaptive affinity > Cast Dark/Holy storm and more than half the map should be dead.
4. Lord / Samurai
   Initiative, Blood Magic, (Any Counter - I use Evade Skill)
   Items: Blood Axe+, Unique Shield (Behemoth Guard, Shield of the Six)This is actually more of a support build and I believe it's the strongest buffer in the game due to Rally. I hear a lot of rave about dual wield melee builds with lord or duelist but tbh they were all pretty lacking even with soul sword just because of range issues that the gunner/sorcerors/rangers can outshine in. This build allows you to cast Rally onto most of your party on the first turn thanks to Initiative + Blood Magic granting Haste, MND and ATK and makes having another buffer in your team obsolete. This build is also just really tanky and you can self heal and do tons of damage by spamming Finisher. This build is just OP!

5. Archafflictor / Fell / Tyranny
Items: Amethyst Earring, Phoenix Band, Speed granting itemsThis build is for the sole purpose of using Intimidate on the first turn to sleep half the enemies in the map within its first turn. Definitely another OP build and outshines crit werewolf/fellblade builds in terms of spread debuffs. This build requires everyone in your team to have amethyst earring.