That's why they call it a Spitfire! The Supermarine Spitfire is a British single-seat fighter aircraft that was used by the Royal Air Force and many other Allied countries before, during and after World War II.
Chinese Stealth Tech- many think China borrowed fighter technology. I also think it would be foolish not to use proven ideas. Plus if your designs can be taken the only main advantages are strategy and training. This where the majors have the edge.