User blog comment:IamJakuhoRaikoben/Chapter 449: Mavis & Zeref, Review./@comment-24264679-20150825020049/@comment-3290324-20150825021521

If it was as weak as you are suggesting it is, Makarov wouldn't have been scared to use it in the Tartarus arc. Plus, Fairy Tail has Mavis on their side as a ghost and her brain works just the same regardless of whether she is in her real or ethereal body. :P