Many religions have esoteric or restricted teachings: Mormon temple rites, the ancient Christian practice of keeping the Eucharist from catechumens, Kabbalah, Vajrayana initiations. Isn’t graduated disclosure common?

The parallel is real. The difference that can be defended is that Scientology’s confidential material contains the religion’s core cosmology, the origin of human suffering in the Xenu event, so that a member commits years and large sums before learning what the religion teaches about the human condition, whereas the early Christian discipline of secrecy concealed the form of a rite whose meaning was preached openly. The Church has also litigated to keep the material secret, which is unusual; the 1985 Christofferson case, where OT III was entered into evidence, is the documentation. The practical point stands: a member may not know this material, and should not be ambushed with it.