This is true. Both characters get a lot more content in terms of sheer word count for the sake of developing their characters. I understand not all characters need to be actual characters, as well. Sera, for example, is meant to serve as a way for players who like that kind of sexual content to enjoy themselves. TiTS is a porn game, so it makes sense. I think there's more to it than just length, though.
Some characters feel like they're hovering in this odd space between the two, though. They're more important than most but never quite reach being a real character. I realize opinions may differ here, but Anno is one such character to me. She has a backstory, she has motivations, she might even have a personality if you look hard enough, but much of it feels like an excuse just to give you a typical shipmate you can screw. You can see the "OBLIGATORY FUCKBUDDY-01" stamped on her forehead here while everything else about her feels almost incidental. I want to repeat that this is just my opinion, though. I know she's rather popular with some people and that everyone has their own ideas and standards involving writing and characters.
I want to contrast this to a character in the Event Submissions section. Kind of cheating, but I do think it's a good example. There's a character named Dr. Lessau being written up by someone and it really reminds me of just a better Anno in some ways. Both these characters work for Steele Tech and knew Victor, and that effects how they perceive and interact with the inimitable Captain Steele.
Dr. Lessau already has more of a connection to the good captain than Anno does before they even meet, and his feelings towards Captain Steele feel more natural even though he currently has less written about him than Anno does. It makes sense that he feels the way he does. Anno seems like she just feels like the way she does because she needs to get on your ship with minimal fuss, and she needs to do that because she's supposed to be a crewmate. When I see Dr. Lessau I can see his actual character motivating him and informing his actions and words, but when I see Anno all I really see is her design.
In short, you are right that Ben/Bess and Embry have a distinct advantage in word count to expand their characters, but I feel the way they were written was what was most important in how they turned out. My post got a tad off-track, but I just wanted to explain what I think was really at the core of how he wrote his most popular characters and provide an example for contrast.