User blog comment:IamJakuhoRaikoben/Chapter 415: And It Shall Become Your Will To Live, Review./@comment-7418318-20150110171453/@comment-9595671-20150115014909

Hmm... maybe, but it seemed like Acnologia was surprised to see Igneel at all, and we don't know how Igneel lost his soul to Acnologia either so we don't even know if they fought. (Acnologia's words do make it seem like he didn't)

I'm not saying that Igneel would have won against Acnologia, but its possible that he would have been more equal in power and could have forced Acnologia to retreat. While Acnologia is the king of dragons Igneel was the Fire Dragon king, so Igneel was likely more powerful than most if not all of the Dragons Acnologia fought 400 years ago,