It's pretty interesting, I was reading what the K*reans were saying about the episode and there's quite a few of them that thought this arc was too mean or disrespectful to Chii, or that it discounted her first season experience too much. I was surprised to see multiple posters with that sentiment, since I haven't really seen that echoed elsewhere.

Personally, I think it would've been weird or even OOC if she DIDN'T get bothered by Vivi's groundbreaking success, especially keeping in mind the whole "people are hard to change" philosophy. I feel like her emotional growth gained from her previous struggles was evident via her solving that inner conflict in a mere handful of episodes, in a way that is ultimately much more healthy and mature (even if it might be seen as embarrassing to bow to a junior and admit your faults), rather than just bottling up that anger for ~40 episodes until it all goes horrifically wrong.