Well, here are some recent (tour 107) "usage" (kills+deaths) stats compared to the respective arena top plane:
LWA
P-39D = 1145
P-39Q = 2396
P-51D = 78398
MWA
P-39D = 161
P-39Q = 293
P-38J = 6637
EWA
P-39D = 171
P-39Q = n/a
Hurri2c = 2328
Apples and oranges. Very few planes will be able to compete with the 51D (or Spits &c) in terms of use.
Let's look at something more comparable, for the same tour:
LWA
Bf 109E-4 = 48
C 202 = 43
F4F-4 = 249
FW 190A5 = 92 (there's a surprise)
P-38G = 123
P-40E = 190
Spit 9 = 110 (another surprise)
MWA
Bf 109E-4 = 49
C 202 = 77
F4F-4 = 295
FW 190A5 = 2231 (no surprise)
P-38G = 592
P-40E = 351
Spit 9 = 3499
EWA
Bf 109E-4 = 72
C 202 = 66
F4F-4 = 569
FW 190A5 = 142
P-38G = 210
P-40E = 273
Spit 9 = 167
Compared to these planes, the P-39 doesn't do so bad.
If HTC creates a new super plane, I'm sure it will get used as much as the 51Ds and Spit 16s and La7s, but the fact is that virtually all of the historically-operational super planes are already here. Any new planes naturally will be used less than the hot rods, once the initial enthusiasm wears off. The 39 has done well because - among its contemporaries - it's a fun plane to fly and fairly capable.
- oldman