A6ms were historically very easy to bring down. They had little to no armor on the early versions, and still very little armor on the later versions.
Spitfires, while nimble and lethal, were not especially durable or resilient. US Navy planes were noted for strength and durability, and in this game they take a lot more punishment. Zeros were not, and cannot take punishment. Each plane is modeled to its real counterpart's strengths and weaknesses.