For a flat spin to develop, you would expect the cg to be aft of the C/L. The cg was probably 20 feet or more aft of the center of the plane - about where the main gear is attached. The plane rotates about the cg.
Regardless, if a tail fin can't stand 100-140 mph sideward force, how would it hold up in a heavy windstorm on the ground?
This descent no doubt resembled a falling leaf more than a rotational spin.
GB