You make a lot of good points here. Kairi's character was sorely underdeveloped, and I hope they take more time with her in KH2. However, there a couple of points I would like to touch on.
A lot of people seem to hate damsels in distress, because they're over done more than anything. But is an over-used cliche really reason enough to hate that individual character? I can understand being annoyed by it, but it's not as if those characters knowingly say 'Let's jump on the damsel in distress wagon' it's more a fault to be held against the game designers. Then you have those that hate the damsel in distress types simply for being weak. But is it really realistic to expect every female to be a strong, gung-ho kind of character? There's a need for weaker characters, too, like it or not. These characters will often have something that gives them an advantage over stronger characters, as well. It could be that they are kinder, more persistant, or perhaps better at dealing with crisises of the heart. Now this isn't neccesarily in defense of Kairi, but as a general statement on the 'damsel in distress' stereo type, from someone that gets kind of tired of hearing them put down simply for being human, and thus, being fallible in a more outwardly visible respect.
Now, for something more Kairi-oriented. Yes, it did seem like she cast aside Riku in favor of Sora, but I'd like to try and give a little insight to her statement on leaving Riku behind. Mere specualtion, of course. Kairi was reluctant to leave, but seemed to be putting on a brave and willing face because she knew it was what her two friends wanted. Of the two, Riku was the one hell-bent on leaving, and didn't seem to care whether or not he ever got back. Kairi, at one point, expresses her desire to return, on the other hand. Perhaps she was frightened by Riku's determination, and was worried that while traveling with Riku, she might not make it back? She mentions that Riku has changed, so this seems plausible. Of course we know that she fancied Sora more, and perhaps she felt safer and more assured leaving with him than with Riku. For someone that cared so much about Kairi, it's funny that Riku didn't seem to notice her fear or reluctance at all, isn't it?
Then, on the idea that Riku could just as easily have returned Sora from the darkness as Kairi... I have to disagree with this. Sora's returning to normal had less to do with Kairi calling his name, and more to do simply with who she was to him, and how she embraced him, willing to use herself to protect him. On the other hand, however, Riku had recently battled against Sora. At that moment in time, there was major wedge between the two. They had taken different paths that pitted them against each other, and at least for the moment left a scar upon their friendship. While they forgave each other later, at that time, Riku calling for him may not have worked. Also, Riku himself had fallen into the darkness at this point. If two people have fallen into a well, too deep to climb out, then one person within cannot pull the other out, can he? It would take someone reaching down from the top. At least, that's how I look at it.
