Elegy for the End is the closest fit on the game's own numbers: Sethos's kit multiplies Elemental Mastery, and a weapon is ranked here on whether its ascension stat and its passive act on that stat. Hunter's Path, Cloudforged and Skyward Harp come next. No playtested ranking has been imported for Sethos, so this is arithmetic over the kit data rather than a damage measurement.
Run Thundering Fury on Sethos, with Celestial Gift and Silken Moon's Serenade behind it. Main stats are Elemental Mastery sands, Elemental Mastery goblet, Elemental Mastery circlet. Roll substats in the order Energy Recharge > Elemental Mastery > CRIT Rate > CRIT DMG.
Talent priority is Elemental Burst > Elemental Skill > Normal Attack. The Elemental Burst costs 60 energy, which is what an Energy Recharge target has to clear.
The strongest team is Sethos, Kaedehara Kazuha, Fischl and Kirara, built around Sethos: Dendro · Aggravate.