OK, then a P-47. What happened was that it didn't come in completely level for whatever reason. The right gear impacts the runway at 30 degress off the verticle, causing it to fold, the left landing gear touches down at this point, followed by the tail wheel. Right wing tip hits the ground, causing the plane to rotate, stresses the left landing gear, causing it to break. Completely plausible scenario, can happen to any plane, and a rough field does nothing to increase the likely hood of this particular accident.
Scenario 2: P-47 coming in for a landing at low speed. Just before touchdown, a gust of wind catches the the verticle stabalizer, causing the plane to yaw 30 degrees to the left, aided by the torque of the engine. Landing gear alignment is no longer consistent with the plane's motion, when the landing gear touches down, they are at a 30 degree angle relative to the runway. This sideways motion is enough to cause a failure to the landing gear. Nose impacts the ground, lifting the rear end up in the air, and the plane flips. Again, perfectly plausible scenario, and one that wouldn't nessicarily be more likely on a rough airfield.
And you are shooting yourself in the foot. If spitfires were that difficult to land when flown by new pilots (I assume they were fairly close to graduation, as they were training in fighters, rather than trainer aircraft). Since these pilots were probably going to be sent into combat soon, they should have been able to land on an improved strip.