I agree, she feels very normal because, like normal people, she has her kinks, but they don't completely dominate her life.
Compare to most of the other LIs, they're all pretty "porny" in their setups- sexy secretary, your old boss, your client- Steph just feels like a regular person that MC met and liked and decided to date, and they're both into kinky sex, but otherwise are just a totally normal couple. Not a lot of games on this site let you just have a regular girlfriend that isn't related to the grand plot conspiracy or some long lost childhood whatever or has some dark secret. (i mean she did have a secret, but it was wrapped up p quick)
Bimbo Steph tho, it's like her life is starting to completely revolve around being a sex toy, which is fine, but it's less unique IMO.