Catholics most certainly are Christians. You realize that other denominations broke off from the Catholic Church, right? Was Martin Luther not Christian until the Reformation? I don't understand your position.
Baptists and Anabaptists were never part of Roman Catholicism, neither were the Heugenouts or the Albingenses, neither was the Aramaic church a part of the Roman Catholic Church, neither was the Jewish Believers in Jesus Christ who worshipped in the synagogue.
There are many groups who were never a part of the Roman Catholic Church.