The Soviets were fond of their P-39s, which makes me wonder about their native products. The 37mm cannon gave them a punch, but they were in the lower half of the class as fighters. Not the bottom, perhaps, but certainly not cum laude.
JR
Soviet Fighters:
'30s:
I-15, I-15bis & I-153. The last Soviet biplanes, manoeuvrable and hard hitting but far too slow.
I-16. An early '30s monoplane, later models were only slightly behind the Bf-109E but outclassed by the Bf-109F. Roughly Hurricane equivalent.
'40s:
LaGG-3: Initially competitive, wartime production quality and weight creep ended up giving it the nickname of Guaranteed Varnished Coffin from the Russian initials.
LaG-5: A LaGG-3 re-engined with a radial (Ash-82/M-82), helped remove Luftwaffe superiority from '42 onwards. Equivalent to early-mid Fw-190.
La-7: A cleaned up LaG-5, the equal to even late Fw-190.
Yak-1, 7 & 9: Competitive at all times.
Yak-3: Superb dogfighter.
MiG-3: Superb high altitude interceptor (400+ mph @ 7000m), but most EF combat was at low level where it lacked manoeuvrability. What finally killed it is that the engine (AM-35) was de-rated (AM-38), used in the Il-2 and thus lost out in production, on the Boss's word.
The Soviets lacked good high altitude power, no turbo-superchargers and in the early days sufficiently trained and experienced pilots. Pilot quality matters far more in an aircraft than crew quality in a tank. High altitude weakness was much less of a problem on the EF, most combat seems to have occurred in the 2-6000m range, quite often lower.
The P-39, though sharing the Soviet high altitude weakness, indeed somewhat worse, had a roomy well equipped cockpit and very importantly a good and reliable radio. It suited the EF air situation. The Soviets kept their few Spitfires and P-47 for rarer high altitude interception. They far preferred the P-39 to the P-40 which was the opposite of Western experience. Contrary to popular opinion Soviet P-39s came with no or almost no AP rounds, just HE. Though devastating against aircraft it only carried 30 rounds and was very slow firing.
One area where the Soviets had a edge was with their MG/cannon. Their pre-war 7.62mm ShKAS fired at 1800 r/m and the experimental Ultra ShKAS managed 3000 r/m, a figure not surpassed until the Gatling type guns from the '60s onward. Their 12.7 and 20mm guns in general had a lower weight than other nations guns. Eg the AN/M2 ROF of 750-850, 28 kg, the Berezin UB 800-1050, 21.5 kg. More bang for buck.