Well actually I'm a stage 4 Club relic holder, halfway to stage 5. So yeah. Melee mage. And Korpg. My SMN is 11 and will be my last Maat job up because it's awful.
This piece will be used for Mystic Boon, Randgrith, and Hexa.
Attack makes a significant impact on anything worth meleeing, since in most situations your attack will not be capped unless you're farming low level mobs, etc. Mystic Boon is not special in this regard. Just like any other melee damage, it is affected the same way. White mages normally do not have much access to equipment with attack on it, making this an excellent piece. DA is not a bad choice either, but she went with Attack+10 for the same reason Amano SAM prefer to WS in Byrnie +1 as opposed to Askar(it's basically a consideration of the +13 attack vs the 2DA, which is not an exact comparison to the +10 here but you get the idea).