You don't know the attitudes are different because we've barely seen anything of her and you're just making assumptions. It's just a cosmetic change, which, if you'll note, all of the main characters have had since the Versus days, some of them arguably more extreme than the changes to Lunafreya. Nobody is mourning the loss of Prompto's white wifebeater or darker and neater hair, are they?

I don't really get your Wakka and Barret analogy at all given that they are actually different characters and what's more, we've actually seen plenty of them to know what they're like and that they're totally different characters. If you want a better analogy, it's like seeing two minutes of you as Daniel on a hike up a hill and then seeing a minute of Loony BoB, EoFF admin, doing some database queries and being all "well that Loony BoB guy sure is boring compared to Daniel!" when you are the same exact person.