User blog comment:Wrath022/Episode 271: Fairy Tail Zerø: Blue Skull, Review/@comment-24277053-20160213171428/@comment-4829046-20160213173329

"giving what happens in the current arc, Mavis hasn't changed much at all"

While you could argue that a spirit is technically not supposed to advance that much in mind as well as body, I think it's more of a case where the bursting confidence she had as a youth gradually became more cynical as the Guild wars continued. Fast-forward several decades and she is in a generation that is stronger and against killing and thus act very differently from the units she used to command back in her prime. Dump the guilt she has accumulated over the years and you get even more reason to make some errors.

All in all, I see plenty of reason as to why she is the way you reference. I may be a fanboy, but let's face it, Mavis is far better case than 'some' others in FT that have absolutely no defense for their bullshit. Mavis and Zeref are like catalysts and thus Mashima elaborates on them a bit more while the rest are separated into typical fields like villain, hero, anti-hero, fodder etc. and even then, only the actual top mages of FT are allowed to pull off the important things despite them having no claim/right to said things. Sure, Sting and Rogue maybe exceptions as per the Tartarus arc, but those two only got that spotlight because they are the only relevant people in Saber that can reform Minerva successfully. If Minerva wasn't there, then the Twin Dragons wouldn't have done jackshit.