I haven't flown the P-38 as often in either AH I or AH II nearly as extensively as some of you, so I can't comment on the differences in flight models between the two versions. From my limited flying of the Lightning I have come to the conclusion that the flight model appears to be historically correct. P-38 attributes evident in Aces High are:
high top speed
excellent high-speed climb
tremendous zoom climb capability
zero-convergence firepower
good maneuverability free of torque influence
excellent range and endurance
above average low-level maneuverability
With such a large number of flexible characteristics I don't believe it is accurate to describe the new flight model as being "castrated."
Some of the disappointment with the Lightning's flight model may come from unrealistic expectations. While the P-38L had boosted ailerons and Fowler flaps to enhance maneuverability it was still foolhardy for American pilots to enter low-speed, low-level dogfights with Japanese fighters. Conversely, it seems that this model could out-maneuver Luftwaffe fighters, although there are isolated voices to contest this (Adolf Galland). Whether this was due to the greater level of experience and training of American pilots as compared to the late-war Luftwaffe pilots is a matter of some debate.
The tightest turning American fighter was the FM-2. Using it as a benchmark with a value of 100, as Francis Dean did in America's Hundred Thousand, America's main fighter types of WWII are ranked thusly in turn capability sans flaps:
FM-2 100
P-63 124
P-61 133
F6F-5 137
P-51D 179
P-38L 205
P-47D 206
F4U-1D 212
While the Fowler flap greatly enhanced the P-38L's maneuverability the difference in turning ability that this flap had to compensate for was considerable.
Regards, Shuckins/Leggern