User blog comment:EvanDude345rv5/Fairy Tail 337 : R.I.P Fairy Tail/@comment-16344653-20130629023710/@comment-1359322-20130630011334

Wendy is still too young to slay a Dragon, wait till she gets one or two years older then it'll be better.

Also Acnologia is on a completely different level from the Dragon, some characters like Gray and Sting have noted that. Also when he was attacking Tenrou Island, he wasn't even using his real strength at least Gildarts mentioned that he didn't even use the strength he used to fight him.