Because Christianity is so philosophically shallow, there is ample scope for debate within its walls. In fact, there is so much scope for debate it is a necessity. The Christian needs a careful measure of debate and questioning to create the illusion for himself that he is not a complete animal: this is the purpose of theology.
The eastern religions, like Buddhism, have greater philosophical depth. Consequently, Buddhists are more secure and sure of themselves, and feel no need for rigorous questioning, or re-evaluation and re-interpretation.
For this reason, the Christians may have a dubious edge on the Buddhists, for as long as there is dissatisfaction there is hope. The Buddhists know a thing or two more than the Christians, but have stagnated in their complacency and self-righteousness.