I wouldn't say they're making Chihaya seem unnecessarily weak, she was weak. Sakura pointed it out very well when she said she was lucky to be playing a girl who was only very fast. Chihaya can utterly dominate B-class, but she's always been hit or miss. If she doesn't get warmed up and fall into a good pace, she doesn't win. If she loses too many of the one-syllable cards, she can't win either.

Chihaya had plateaued by relying only on speed and her reaction time. She's always had these weaknesses, as the upside down game she lost to Taichi proved. Now that she is playing against experienced A-class players, it's becoming that much more evident. High schoolers rely on the same methods (speed and memorization), they haven't tended to use much strategy either.