Fairy Tail: I Can Use Enchantment Magic

Can the protagonist know dragon-slaying magic? If you can learn additional magic from Irene, you should also be able to learn the Holy Dragon's dragon-slaying magic, right? The protagonist is useless, and it is said that the protagonist is Erza's brother and he helped Erza use additional magic to create armor weapons that are stronger than those in the original work. As a result, Erza's strength has not changed at all in the Iron Forest plot, which is no different from the original work. If the protagonist as the brother really helps Erza become stronger than the original work, then Erza can defeat those little chicks in the Iron Forest alone, so she still needs help?

Very good, hope everyone is well