I also now believe that Oswald alone shot Kennedy, and for the same reasons as you.
I do, however, believe the theory that Secret Service George Hickey in the car following Kennedy accidentally delivered the head shot in the chaos of the moment:
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How can Oswald have alone shot Kennedy while at the same time Hickey shot Kennedy in the head?
I am referring to the intentional shooting by Oswald. George Hickey did not shoot Kennedy intentionally. He never would have picked up the rifle had Kennedy not been shot.