Yeah, they even kind of admit it in the Iwata Asks of Fire Emblem: Awakening during the section they talk about the involvment of Kozaki Yusuke as a character designer...
I have thought abut this for a long time, but I think even Senri Kita involvement in her games is also to follow aesthetic of the time. FE9 was released on Game Cube, and on this particular time frame we have games such as Suikoden 3-5 that have similarity in aesthetic of the character design. I'm still searching why this is case for that era, but I still can't find it why such (good) aesthetic is popular in the era.
No, they both come from exactly the same place. The dark, "evil" side with skimpy clothes because sex is evil and purity is innocence is a trope that spanned even all the way back to the story of Adam and Eve. The only difference is that you can choose to be part of the dark side in this game.
That's a good point. But still, even Aversa have more "common sense" to her design. She's a more of a spellcaster character, and "part" of dark mage class line to boot. She wear scanty clothes, not mail or armor that shaped to her boobs and apparently can jiggling too. And even she does not show her thong ffs.