Q u o t e:
The design is for bears to be viable, end-game main tanks. The design is for cats to be viable, end-game melee dps. In both cases you are going to need the right talents, good gear, skill and companions who can back you up -- I don't mean to imply raiding will be easy.
If you want to do a little tanking and dps, you probably won't be as optimal at either, though you'll probably always be better at switching between the two than other classes. In order to be as good at tanking as the other classes, you might have to give up a few talents that maximize your dps, and vice versa. This is a good thing -- it lets you choose to actually be a main tank.