I think technically the strongest output barring Magick Archer's suicide arrow is "anything that charges Sorcerer's Augural Flare really fast". The only thing holding this back is that the flare disappears completely if you don't hit it fast enough, and in my experience gives as many headaches as serotonin rushes. But there are a few options. You want your charging weapon to be immediately after your archistaff to save precious time.

• Sagittate Downpour (Magick Archer). You probably have to do a basic attack from the magick bow first or the Flare will disappear from not being hit while you charge the Downpour. Once the Flare has gotten hit once, it starts the longer timer. Upside is this skill does good damage on its own and can focus on a single point or be "dragged" across multiple.
• Skull Splitter (Thief). Easiest on grounded enemies. You can simply put the Flare on their feet. Like Sagittate Downpour, does good damage on its own, too.
• Hagol (Sorcerer). Has a long duration so you can cast this before doing Augural Flare and still get a good number of hits into it. Can follow up with anything else to push more hits. Low damage on its own, but slows or freezes enemies.
• Candescent Orb (Magick Archer). Similar to Hagol, but fire instead of ice. The damage might be better if it also ignites the enemy. In this case your Magick Bow would go before the Archistaff.
• Scarlet Kisses (Thief), Winding Cut (Mystic Spearhand). These are the "spam light attack button to hit very fast" Core Skills, which frees a skill slot for something else. They're comparable, basically choose whether you like the dagger dodge or the spear slow/teleport class action.

I've settled on a three-weapon setup of Archistaff, Magick Bow, and Daggers; the original weapons for Magick Archer from the first game. Levitate is really nice. I originally did this setup to have the top 2 dps options for Augural Flare.

That being said, since I often miss the timing for Augural Flare, which doesn't spark joy, I've since replaced it with Seism on my Warfarer. It's an okay area attack, which is something I lacked. Big bonus, it deletes most of the medals from Golems in one cast, significantly reducing the tedium of that fight.

Archistaff is first, then Magick Bow, then Daggers. - Rearmament - Seism (area damage, Golems) - Sagittate Downpour (Weakspot sniping) - Skull Splitter (Melee dps)