User blog comment:FairyRaven/Fairy Tail Chapter 435 & 436: The Cry of Victory & Memoirs, Review and Commentary/@comment-24277053-20150518124050/@comment-9595671-20150518143805

Its heavily implied Zeref is weaker than Acnologia though, so I'm not so sure on that.

Remember, Future Rogue stated his timeline is basically ruled by Acnologia. That seems to be where the story is going towards canonically, we don't know what's changed yet though and what happened to get to it either.