I think it needs less of a buff to raw DPS (though it is a bit RNG-based and such), and more of a boost to DPS consistency when motion is involved.

I also think it's a mistake for Foe Requiem to only boost magic damage, and think that there should be some kind of inbuilt boost (like Disembowel or Dragon Kick for instance) since balancing potential DPS output around a Bard being present and able to use that one specific song just seems problematic. I would rather Foe Requiem be retooled to boost all damage (by an amount <10%).