I’m sure I evaluate the Bible differently from secular scholars in some ways, but for the purposes of these two lectures, it really doesn’t matter. The things I lay out are things that there’s broad agreement on. (Plus, you might consider the possibility that a Christian’s faith stems from his coming to the conclusion that the Bible is a reliable source. In other words, the cause and effect could be different from the way you’ve framed them.)
Secular scholars will use the Bible to teach Hebrew history as well. As I said in the lecture, there’s not much else to go on for most of Hebrew history.
The purpose of the two lectures is to help establish the importance of the Hebrews in the history of Western civilization, I think the conveying of the Biblical narrative is the best way to accomplish that. Whether or not the stories are authentic, the simple fact is that for about 1,500 years nearly everyone in the West accepted them as true, and they helped to shape the way the civilization developed in a number of important ways. So it’s important for a student of Western civilization to be familiar with them.
I hope this helps to explain why the lectures are structured the way they are.