The first rpgs, like the American "stovepipe" and the German "Panzerfaust" did not appear until 1942, but since both the tanks and the carriers in Dogfight are late WW2 style, I don't think that would be a problem.
The idea of a light bomber with a crew of two or more, like the French Breguet or the British Airco, would also be an interesting idea.
Rather than giving the top players better planes or guns, making them even more (and unfairly so) difficult to shoot down, I think giving them the possibility to command a group of men in a bomber would be more to their liking.
But don't forget the zeps! Arming them with two machine guns, giving them a historically correct 4000m / 1200 ft max altitude, and giving a top player the command over them, would make them a realistic challenge.