Nor did I reduce it. I used a particularly egregious example. But I challenge you to find where in that book he unpacks that argument further in a way that acknowledges the concerns I raised.
It has been many years since I read “Mere Christianity,”as evidenced by the act that my paperback copy is a 1979 imprint and is turning yellow. Looking at it casually, I gather that he has not the slightest interst in your “concern.” He is not “proving” anything in this book but simply explaining what traditional Chirstians, whether Catholic or Baptist believe. I think you are misled by a rhetorical flourish (pp.55- 56 of my copy). He has spent some time on the great war that is going on in history, between good and evil, and at the end basically dismisses the view of liberal Christianity as a great moral teacher. The tone of the New Testament does not convey any such mushiness. The figure presented by the writers is not such person. The person of Jesus as understood by traditional Christianity is something other than the Jesus of Jefferson’s Bible. From the perspective of the atheist, such as Lewis once was, this person is a loon., or someone to whom absurdities are attributed. . From the perspective of the Christian, which Lewis now is, he is God.