Protestantism

This is not a historical account of the development of Protestantism. Like all of my religious books, it is an exercise in logic. 2 Thess 2 deals with the Antichrist and a falling away from the True Faith prior to the Second Coming of Christ. If the Church of Rome and the Eastern Orthodox Church haven't fallen away from the True Faith, or at least if one of them hasn't, how could Protestantism make any sense? If they have both fallen away, if neither one is the Church which Christ founded on a rock, Matthew 16. 13-19, if both lead people to perdition, then one might certainly turn to Protestantism in one's search for the True Faith and True Church. Is any church under the sign of the cross the True Church, the Church which Christ founded on a rock?