Let's be clear on our terminology and our hierarchy of relations. Catholicism isn't "different" from Christianity. Its a subset of the general Christian set of beliefs, and so are the various Protestant denominations.
They differ on specific beliefs and interpretations, but there's no one denomination that can be demonstrably proven to be more "Christian" than any other... If ANYTHING, Protestants broke off from the original Catholic church, making it the more fundamental one, but even that's ignoring the changes that the catholic church itself has gone through in its history.