User blog comment:Miskos3/Fairy Tail 535: The Greatest Power, Review/@comment-86.70.179.188-20170512143000

Even if the fight isn't perfect, i don't think Mashima want a physical defeat for Zeref, he wants a psychological one, nothing else, this is why the fight is build like that and is linked to Acnologia fight with Pegasus and co., maybe Mashima's idea is the fairy tailisation of Zeref, and Zeref who choose to destroy Acnologia and save Jellal.

The rewriting of END's book is also a clue pointing to this end, imagine : Zeref the guy who lost everything, who was cursed because of his sorrow and anger, who is the one behind all problems, chosing to destroy Acnologia by sacrificing himself and thus giving his little brother a bright future, it will be wonderful, evenif if I think Zeref's sacrifice will be for nothing, and the dragon slayers will have to fight Acnologia