I understand what you're saying, the dumb and bratty sister has been done before. Frankly, I love it. Lol. Always seems to work for me. Nothing wrong with your opinion, but it certainly illictited a strong emotional response from you as seen from your lengthy post about it. So the dev succeeded in that sense. Won't you be happy when the MC inevitably breaks her and has her worshiping the MC(my opinion, not sure if that's the plan)? Also, out of curiosity, how would you prefer her demeanor to be?
It's not just dumb but unbelievably dumb. I mean the whole way she is presented is like I said what you would expect from a maybe a 12 going 13 year old spoiled girl who thinks she is all that not a grown woman. The trope of a mean elder sister just honestly never made any sense, because it is not just sibling rivalry but it often makes them seem like a villain in a sense for no reason. I always ask what did the MC do in these games that justify them acting like that. It usually just ends up with the answer being they just are and that just means they are a horrible person. So in games like that I usually skip those characters or if given the option for a revenge route or dominate route I go that way and then just use them and throw them away, because of the unjustified hate they show, so I hate them back. Any negative option I get concerning them I pick it.
I had an ironic moment when I was thinking if I ever do anything with this girl it will be a wham bam thank you ma'am situation then 2 seconds later she said it. Probably she gets that treatment because that is all she is worth. I can't speak for the goal of the dev on what he was trying to achieve with this character, but it my case it didn't make me even want to break her or worship the MC, or have anything to do with her sexually. It made me hate her and just want to put her in her place. Possibly even go so far as use my influence to wreck her life and show her what real power is. Maybe have her boss at work turn out to be one of the MC's women and make her life a nightmare and then lose her job. Give her a cold hard slap of reality across the face both physically and metaphorically, and have a serious reality check, that this ain't first year high school and it ain't mean girls. Maybe have Anna torture her a bit as her new toy.
In terms of your question how would I prefer her demeanor to be? At least a decent human being, because right now she has absolutely nothing redeeming about her except for her friend. There have been games where we have had tough girls in appearance who were either bikers or police with alot of tatoos like her but turned out to be absolute sweet hearts while maintaining the rough girl appearance. Plus no way in hell she made it past basic recruitment much less detective with her lack of intelligence.
The reason why I talked so much on this is because this is like the 5th game in a row that I have played with an older sister like her and for some reason they are all brain dead jerks who are mean to the MC for no reason. I was like seriously again?! So it finally got tiring and I poured that resentment into this.