Er, a minor nitpick but in your original post you mentioned giving Faith to a PLD who's currently in their Requiescat phase while the party's RDM is doing their melee combo. RDM's Enchanted weaponskills are still pure magic damage, so they'd still benefit an absolute ton from Faith at that stage (let alone Holy/Flare and Scorch being magic). The way you can tell is whether the ability says "Delivers an attack" or "Deals unaspected/wind/fire/etc damage". If it's the former, it's physical, and magic attacks are always the latter. The only exception is Dragonfire Dive, which is both physical Piercing and Fire damage.