Back in retail vanilla, if you wanted to go balance (and no one did, except the masochists like myself), you went feral until 41, then respecced to Balance with Moonkin form.
Even then, however, it is slow. On a plus, gameplay is exactly the same from 40 to 60 and onward. The only things that change at 60: better mana recovery (reflection), and the addition of Insect Swarm. However, Insect Swarm sucked. You would mainly just spam Starfire and Moonfire. Wrath pretty much didn't get used.
And, didn't need to be Cata. Moonkin was wicked when BC came out. I regularly was near the top during raids. Some fights were horrible, however, due to the lack of threat reduction.