I guess my take is that while technically the early war spitfires and me109s were comparable, by the time the Mark V and later spitfire models came out, they were becoming technically a stronger plane. Add to that better training, fuel, logistics (parts, maintenance, etc) and I think the unit merits a better combat value. Keep in mind that while the unit is represented by a miniature, it actually represents around 300 aircraft and everything around the combat aircraft.
I wanted to represent the general qualitative edge in airpower moving toward the Allies as the war progressed. An argument could be made, however to have Hurricanes be a 4 air-to air and early war spits to be a 5 - but I think it is additional complexity that is not needed.
Open to discussion and debate on the topic though - very much like your suggestion on the addition of the mechanized artrillery piece for the Germans. . .that came in very handy in the last game we played. . .
