I do almost your method, except I do the presentation a few times as practice to make sure the flow works. When I give the presentation it's not scripted, but since I practiced it is much easier for me to improv. My slides are typically very sparse and simply act as a trigger for which part of the topic I'm speaking on at that time.

But, to your point, I agree that your method is the best way if you know the subject matter. When I practice it's mainly for transitions/flow and not the information.