I don't know what it will take for you to realize Fairy Tail is one of the worst manga's of all time. Horrible fights, terrible character development, and in the case of the fights, it doesn't matter the power difference, because Natsu will literally be getting destroyed, think of his friends, and one punch knock out the villain. Look at two chapters ago. Erza getting stomped, loses her eyes and all of her human senses. Still wins! And it literally said "Because she's Erza". It's a joke of a manga. If there's one manga that Kishi referenced in the final chapter, it's One Piece. He basically passed the mantle.
It is a great manga if you look after a series with plot, good storytelling, and well developed relationships between characters.
As you give as example the fight with Erza, it looks like you care very much about fighting.
Take it this way.
Erza cares so much about her friends, that nothing can stop her to protect them.
She would even surpass her own limits, even do the impossible.
How is this bad development or bad writing...
Take the last chapter as an example.
Gray comes back to assist Natsu and also gives him back his lost scarf.
Gray tells him if something is important to him, he should not lose it again. He talks about the scarf, but only about the scarf...?
But if we analyse a bit the saying and the situation, we can see how deep was the message Gray told Natsu.
Natsu was apart from Gray, Natsu needed his help and Gray found him. Gray got separated from Natsu, so he lost him for a moment.
Gray was also referring that Natsu was very important for him, and that he wished to always be on his side, to help him. He was not only talking about the scarf.
There is a great development of their relationship, and this only in some pages.
To understand something from this series, you have to understand the characters' feelings.
Dialogues have very deep meaning as this is a manga focused on storytelling and emotions, friendship, etc.
Fighting takes the second place.
