Carbon is wonderful, expensive, light-weight.. and brittle.
She don't bend... now.. I don't recommend bending your rudder shaft... but snapping one off is even worse. Aluminum works, is lighter than brass and you can gently bend if back if you step on it and bend it (NOT that I have ever done that of course) and have a chance to keep racing until you get back to the shop and replace it.
Brass is a little heavier, and a little stronger and a little more pliable... because you can break the aluminum rod if you step on the rudder AGAIN and bend it worse (NOT that I have ever done that) and break the #$%$#^#* thing off... because you forgot to put a new one on when you got back to the shop (NOT that I would do that)