So far I think the author's progression is purposeful and makes sense. The more Reirin shines (especially in Kei's body), the worse Keigetsu feels about it on the inside, and it's reached a tipping point for their friendship. But I think this is probably the best turnover time for Keigetsu to prove her point that Reirin is reckless, and for her to start gaining more confidence in herself.
So far I think the author's progression is purposeful and makes sense. The more Reirin shines (especially in Kei's body), the worse Keigetsu feels about it on the inside, and it's reached a tipping point for their friendship. But I think this is probably the best turnover time for Keigetsu to prove her point that Reirin is reckless, and for her to start gaining more confidence in herself.