Pyrrha was an annoying personality and the gameplay replacement for Sophitia/Cassandra. Namco essentially forced us Sophi users to play Pyrrha, and it wasn't satisfying. The signature Alexandra stab punisher had much less range than her Mom's. Folks like Siegfried could potentially out-space her in ways that wouldn't fly against Sophitia. Pyrrha needs her Critical Edge to punish outside stab range, which can be annoying. Add in her obnoxious whining, and squeaky voice "CAN'T STOP!", and she fails her Mom and Aunt.
Obviously, she was one of the best characters in the game though. Most pro-players ranked her A-tier at worst, she had even to favorable matchups nearly across the board, and the tournament presence to back it up.
Dr. Hates said it best,
"This character [Pyrrha] basically has no weaknesses. While some characters can do individual things better than she can (e.g. damage output, space control, etc.), it’s really hard to compete with her as a total package. She’s designed such that the best way to fight against her involves spacing, but the movement system (highly unsafe backdash, almost totally safe forward dash) makes this disadvantage negligible."
Still, gameplay strength isn't everything, and I'd rather play Sophi/Cass.