User blog comment:IamJakuhoRaikoben/Chapter 433 & 434: Ikusatsunagi & Demolition Fist, Review./@comment-24546844-20150511182459/@comment-25111584-20150511222011

Actually, they pretty much stated that they had all already been defeated by Acnologia as he was the one who removed their souls from their bodies or whatever. So I'm pretty sure Igneel was not stronger than Acky.