Well Alexis, Nikki and Cara only have the most content so far. In terms of romance and story Layla is close to them already and the future is starting to look bright for Valeria fans, too. Especially Erynn will probably get a lot more content before the game ends. But I agree with you. Some characters are just worse off than others.
It's a little disappointing that Zach points don't have a use and that the other women don't have anything that compares to going to the concert with Alexis. It seems like Alexis and Elena are the only characters with interests and personality outside of school or work. Even Nikki and Cara could use some work, because, besides the different scenes, they're basically the same person now. Nikki suddenly being all timid, when she comes to visit is a little grating.