The one place I'll disagree with you on there is the Japanese. They may not have fielded as many aircraft of a given design as we did, but they fielded a large number of designs due to having the Army and Navy use separate designs like we did. The problem with the Japanese aircraft is performance data is hard to get.
Still, there are a fair number of Japanese aircraft that should be added, starting with the Ki-43-II.
Been a while since I've looked at this, but IIRC the Ki-43 I-III could all be done just with different gun packages.
The A6M3 would be a good mid-war fighter to add, along with multiple gun packages for the A6M5 to represent the a, b and c versions. Include the N1K1-J as an mid-war option for the George, and you can add several Ki-61 variants just with gun packages. G4M is an absolute MUST, while the Ki-44 and Ki-45 would be invaluable to round-out the IJAAF (interceptor and Heavy Fighter, respectively). Add the Ki-100 for another late-war fighter option alongside the J2M. Then toss in the B6N and D4Y for mid/late naval strike craft.
Probably the BEST lineup for the Japanese to cover the full range of the war would be:
IJN
A5M
A6M2
A6M3
A6M5a/b/c
A6M6 (I still argue there's enough evidence for the Model 53).
N1K1-J
N1K2-J
B5N
D3A
B6N
D4Y
J2M
G4M-1
G4M-2
IJAAF
Ki-21
Ki-27
Ki-43 I/II/III
Ki-44
Ki-45
Ki-49
Ki-61 (multiple with gun packages)
Ki-67
Ki-84
Ki-100
With more options for bombers I would arguably perk the Ki-67, owing to its extreme speed and defensive firepower (unless HTC wants to add the all-20mm armed G4M).
