You know, Cassandra was intended to replace Sophitia. That's why she initially had the same color scheme and shared a lot of moves. She was a successor character, just like Yun-Seong was to Hwang, Natsu was to Taki , Xiba to Kilik, etc. ...
That said, I think she's one of the best successor characters in the series. A great mix of familiarity and new ideas.
But Namco fucked up by not actually having her (their best replacement character) actually replace Sophitia. I like Sophitia, but Cassandra really deserved to have the spotlight as the only Greek warrior lady in SoulCaliburs 2 - 4. That way, Sophitia's return in SC6 would actually feel hype. And Cassandra fans might be less upset about their character (maybe) missing two games in a row, since there's a precedent for having only one Greek warrior lady.
Alternatively, they fucked up by not including Hwang in SCs 2-4, but we all knew that already.