User blog comment:Miskos3/Episode 272: Fairy Tail Zerø: The One Who Teaches Magic, Review/@comment-190.58.249.5-20160221003339/@comment-5303512-20160221183054

It all depends on the villains that eventually turned to the good side.

It takes more than just training alone that can make a difference, there is also the good conviction as well.

Erza Knightwalker sure maybe strong and devoted but she was more of a blind puppet to those beliefs that she could not see the suffering of others that she was causing and even hurt her comrades. Even though she does not have any magic makes it harder to wrap around.

Byro maybe strong, by he is a blind puppet as well to his cause and lacks the bond with his comrades that he is willing to sacrifice his comrades for their "blasphemy".

Acnologia, I cannot say since we do not know much about his past, but all we know is that he treats humans as low as insects and don't even talk to them. But is so OP strong that is not arguable that lived up to the hype so far.

The only antagonists that may lean close to the "strength of feelings" is Sting, Rongue and Yukino since they have people important to them, although they were in the "old" Sabortooth with arrogant ideals and belief in self importance and treating your own comrades like nothing special.