heating and rapidly cooling any kind of metal will change the composition of it. i'm guessing since both the hub and rotor both get heated and cooled pretty much at the same time they'll both become more brittle.
i've got an 85 warrior, 85 pally, and 77 huntard. horde, play on Lightbringer.
and idk whether i'm excited for the pandas or not, i think i could grow to like it