Garuda's Spine wins for BRD. Sure, ARC/BRD damage is significantly Light Shots, and although they may hit a bit less with the Spine than with Ifrit's, you can throw them out more often. The DPS value speaks for Light Shot damage as well in the sense that doing nothing but LS on every cooldown you'd do higher DPS than with Ifrit's. Being that the DPS value is higher on the Spine, you also do greater damage on weapon skills with the Spine.

Overall I don't see the Spine being beater by any bow on BRD due to the magnitude at which DPS effects damage done compared to other stats/atributes.

It's also for this very reason, DPS, that Sarnga +1 is best for ARC.