Well that's not entirely correct either. Sure, the plot of the series itself was only advanced in the end (and significantly enough to warrant playing, mind you), but there was tangible character development on Riku's part for the series. It also introduces new worlds, and advances the plots of old ones. If KHII was any indication, KHIII will play off of those furthered plots. All in all, it was one of the most important non-main series games. More important than CoM, even.
I think that the logic prompting the post was that she's a Replica. She's not like Sora, Riku, etc. She's got one other character even remotely like her (Riku Replica). When you consider that, this is a viable argument.
