It's just a concert performance that they'll only perform a few times and never do again, so they don't practice it until it's perfect like they would if was their own song. Despite that, I thought the singing was still better. Obviously, not the dancing.

The only singing that I thought was not as good or better was Karin doing Sakura's big line. It was good, though. Just not
as good. But that line is right in Sakura's tessitura, not Karin's, so... yeah.
Berryz - Crazy Kanzen na Otona
C-ute - Watashi, Choito Kawaii Urabanchou (loved this)