Part of what you want to see is already there - differnt characters react differntly on the various kinks.
Some want to stay slim or even sporty some enjoy gaining and becoming more of themselves. Some are afraid about gaining - and yes some like it at first but then think it is too much or vice versa - so some girls are already going through different emotions and change their mind on the journey!
I think there is a lot of variety already there, and the developer is on a very good track to add even more personalities/characters in future!
I would not change the personality system at all, becasue it is beautiful as it is!
The game is about changing the characters bodies and then see how their mind reacts!
If you could convince every charcter to behave the same way that is simply boring because repeditive.
Not every character will be the right one for you but some character you dislike will be the right one for someone else! No need to even their behaviour out and kill variety in the process.
Ofc more personalities are better! But please do not messs with the already existing ones!