Maybe your definition of a one button wonder is different to mine, but as far as I'm concerned, any class/spec that relies disproportionately on one spell to kill stuff is a one button wonder. That's FB killing ferals in my book. Having to build 5cp doesn't change that.
As for the comparison to 5.2 prot wars with SS, imo ferals are worse. SS never hit me as hard as FB does. With SS a decent player could survive and recover if they played right. FB on the other hand is so strong that survival is unlikely, never mind recovery. From a pvp standpoint that's just wrong, and should never happen.