Exactly right, reverse corruption is the term I would use for Jin's story. This doesn't mean she won't be sexual though.Jin's route is unlike most others in the game.
Take Autumn for example. It's pretty clear her route is a corruption focused one. The classic turning a sheltered religious girl into a whore.
Jin is the opposite. It's reverse corruption. Lin doesn't care if she is sexual, every girl in the game, including Lin, are very sexual. In my game all the girls that have the slut outfit wear it around the hotel (besides Emma, I like her casual outfit more).
The difference between Jin's sexual behavior and the others? Love. Yep, you heard it right. Jin is overly sexual because she is an addict. The other girls are overly sexual because they're madly in love with MC. Lin wants Jin to have that kind of experience, to be loved. Not degrading herself as a sex addict like she was. To be sexually free but in a loving way.
Jin sort of reminds me of Maria and Ashley. Two other girls who were very sexual, but for the wrong reasons. Ashley because she believed she had to be that way to be loved. And Maria was similar, she didn't value herself. They both changed later in their stories because they fell in love with MC.
As far as Jin's look changing. I sort of agree, I don't think it's bad but I do think it's too drastic. But maybe that's the point. She started on the far side of the spectrum and ended up on the opposite far side. Something closer to the middle would've been better. Something more revealing, but in a classy way. She still says she is feeling horny when you talk to her, I don't think it makes a lot of sense for her to cover herself up completely. She is still a sexual person, just not an addict. I also don't think the body change makes a lot of sense. She lost weight when she cured her addiction? Most addicts are the opposite, they gain weight because when they were addicted, they neglected other parts of their life and health to focus on their addiction. She wasn't a food addict. Although I believe Runey has said he likes smaller boobs, so maybe Jin's change is just his personal preference and he needed a reason for it.
Jin was taking Dark Elf hormones, which made her body very similar to that of a Dark Elf. Common Elves are usually very petite, with Nia being one of the most well endowed in that area. So I do actually consider Jin's current state to be close enough to a middle ground between Dark Elves and Common Elves.
And yep, as I've stated, I personally do not find that body type attractive, but with a reverse corruption theme and her new "sisterly" look, I quite like her. The reason Jin hasn't gotten much content previously is that.