I see what you mean, though I actually felt it was the opposite about the pitch-perfect thing. Especially in episode 5 when Hibiki's showing off her new moves for the first time, I actually thought she sounded like she was moving while singing? Oh well. But yeah, the team behind the series (Elements Garden) is a music team first and foremost, and their goal was music-oriented, so it's entirely possible some writing quality was sacrificed for the sake of music.