Vivid Notions is the closest fit on the game's own numbers: Yanfei's kit multiplies ATK, and a weapon is ranked here on whether its ascension stat and its passive act on that stat. Reliquary of Truth, Royal Grimoire and Nocturne's Curtain Call come next. No playtested ranking has been imported for Yanfei, so this is arithmetic over the kit data rather than a damage measurement.
Run Crimson Witch of Flames on Yanfei, with A Day Carved From Rising Winds and Disenchantment in Deep Shadow behind it. Main stats are ATK% sands, Pyro DMG Bonus goblet, CRIT Rate / CRIT DMG circlet. Roll substats in the order CRIT Rate > CRIT DMG > ATK% > Energy Recharge.
Talent priority is Normal Attack > Elemental Skill > Elemental Burst. The Elemental Burst costs 80 energy, which is what an Energy Recharge target has to clear.
The strongest team is Yanfei, Xingqiu, Sucrose and Bennett, built around Yanfei: Pyro · Vaporize hypercarry.