Peter Gunn
Master Sergeant
I see what you did there, well played sir.In September 1940 only the P-40A, YP-39 (without turbo), YP38, F4F-3 were in production, or in near production. Additionally the X73 (prototype Mustang I) was poised for first flight, XP-47B, XF4U were making, or about to make first flights. Start of design for P-63 was six months in future.
The XP-46 was proving a failure and Curtiss was slowly losing ground as a Pursuit name. Army ordered more P-40s and feedback from Britain and France were pointing out serious deficiencies of export P-40/P-39 as combat aircraft for ETO. RAF engaged early to ensure that NA-73 would install such features for Mustang I.
Allison still locked in to single stage/single speed engine - and Army still wedded to in-line/turbo supercharger systems for high altitude performance but about to test R-2800 w/Turbo in XP-47B.
Short answer. In September 1940, the US was scrambling to mobilize from small core of Officer/NCO/Enlisted man (ALL Services) to a massive Citizen Soldier Army/Navy. From making razor blades and automobiles to Liberty ships/CVA/BB, 6x6/Jeeps, obsolete aircraft to hold the line, 1903 Springfield to Garand, High School QB to fighter pilot - and still had Pearl Harbor and PI and Kasserine Pass in the future.
We were long on base assets but woefully short as warriors prepared for mechanized warfare in three dimensions. On that scale the A6M was a minor annoyance.