[C.A.]

Well its easier to agree and more fun to do that lol

Yuki is the same in the novels, just that everytime Kyon enters the club room, he either doesn't mention her at all or just leaves a line saying that she's back at her seat. If you missed that line you forgot that she's there, that's exactly how Yuki is and Kyon has said it throughout the novels/show, that you won't notice she's there or she said something unless you put in an effort to look/listen to her.

But in the show it magnifies this effect because Yuki stays in the screen all the time and she's either out of focus or covered by foreground characters. And somehow we notice her because we are such powerful observers and shows that we really put in an effort watching the show lol

So in both novels and the anime, Yuki spent the most of her life doing 'nothing', just that in the novels you totally forget her presence in the room and in the anime we get to see that she's actually there but doesn't matter if we don't notice her.

EDIT: About Yuki's development, actually Yuki is also the 3rd most developed character through the anime after Haruhi and Kyon.

Yuki changed from the usual specs+uniform+cardigan+book combo to a range of other clothes and starts using computers. She found that computers are fun and wants to join the computer club. She found trust in Kyon and always gets his permission before doing something. She also learnt to help instead of ignoring.

Mikuru and Itsuki almost has no development compared to Yuki. Mikuru wasn't too bad, she develops certain feelings for Kyon, but Itsuki is himself from his first appearance to the end, except that maybe he found SOS-dan was fun.