That's a common belief, but it isn't true. The details make all the difference in the world. Just like Sophitia and Cassandra don't really play alike, neither do Amy and Raphael, Sigfriend and Nightmare, or any of the other "Clone" characters. While they may possess similar animations, or even similar weapons, their effective tactics, frame data, combo's and such are wildly different from one another once you look just beneath the surface.
-Idle