User blog comment:FairyRaven/Fairy Tail Chapter 401: Igneel vs. Acnologia, Review and Commentary/@comment-77.194.131.12-20140922125827/@comment-7418318-20140922133219

I agree on that.

Also it was said that E.N.D. was the strongest Demon Zeref ever created. That doesn't leave much room for multiples of their kind, unless the other three are weaker than the flame one.