Being kind and being submissive are not the same, and even within these traits, there are different "flavors".
The first question you should ask when introducing new variables is what they should accomplish and if they support your story. Oftentimes, developers make the mistake of introducing personality variables because they like it and want to give the player a choice, but then they have to develop story lines that they themselves do not like or that do not fit in the story, which leads to bad results. This should be avoided.
So for example, if you imagine on of the girls being "kind" it doesn't make sense to have a kindness variable for her, because she will always be kind.
However, if you want to develop two versions of Elena, one dominant, one submissive, it does make sense to introduce a dominance / submissive variable. Of course, you could also imagine Elena being submissive by default and having the choice about what kind of submissiveness (bratty, eager, reluctant, non-con etc).
So your variables shouldn't determine your story, your story should determine the variables. What's the story you want to tell, what are the branches and variations, and based on that, what variables are useful to determine the storyline?
Examples:
Another topic, you asked somewhere else what we expect in a story with cheerleaders, so that's also something I wanted to answer: