Why not go back and kill Caesar instead and prevent the Roman Republic from collapsing into the Roman Empire?
Why not kill Charlemagne and let the Moors roam Francia?
Why not kill Christian IV and let Denmark keep Skåne, Halland and Blekinge?
Why not kill Louis XVI and hope for a better king to prevent the French Revolution?
Speaking of which, why not George III?
And if we are going to talk about Hitler, why not kill Bismarck to prevent the unification of Germany which set the pieces in place for the First World War, which led to the Second World War.
Why not Napoleon for that matter?
There are so many more interesting choices to kill, all of which would prevent Hitler from becoming relevant. And monarchies would control the world to this day.