User blog comment:IamJakuhoRaikoben/Chapter 471: Until the Battle is Done, Review./@comment-5303512-20160202131244/@comment-7418318-20160203084740

Considering that the tripple-combination Roar of Natsu, Gajeel and Wendy didn't leave so much as a scratch on Acnologia on Tenrou, I doubt that's the case.

It's not like Dragon Slaying Magic does more damage to Dragons than other beings, the only advantage of DS Magic is that it can cut through this mystical defense of a Dragon that making them practically immune to regular magic. But even that only seems to work partially, since DS magic still does more damage to non-Dragons than to Dragons.