Originally posted by Kevin14
But were the P-39 and 63 really that good? Why add airplanes that no one will fly because they're not that good? We could use a Ki-84 (and the Italian G.55 or R.2005) that people would actually fly.
The P-39 was not a very good plane for the U.S. It was outturned in the Pacific by the zero, and NACA's decision to leave off the supercharger meant it was lousy at high altitude performance in the european bomber escort or interceptor role.
But the Soviet Union liked it because it was a great tactical ground attack fighter with it's 37mm canon. They also did very well with it in low alt dogfights. For an interesting discussion of the P-39 from the SAF point of view, read
http://airforce.users.ru/lend-lease/english/articles/golodnikov/part3.htm Here's a quote:
"A. S. Nikilay Gerasimovich, could the Cobra really contend with the Bf-109G and FW-190 in aerial combat?
N. G. Yes. The Cobra, especially the Q-5, took second place to no one, and even surpassed all the German fighters.
I flew more than 100 combat sorties in the Cobra, of these 30 in reconnaissance, and fought 17 air combats. The Cobra was not inferior in speed, in acceleration, nor in vertical or horizontal maneuverability. It was a very balanced fighter.
A. S. This is strange. In the words of one American pilot, the Cobra was an airplane “suitable for large, low, and slow circles”. To go further, if we judge by references, then the maximum speed of the Cobra fell below that of the Bf-109F, not to mention the later German fighters. The Allies removed it from their inventories because it could not fight with the “Messer” and the “Fokker”. Neither the British nor the Americans kept it as a fighter airplane.
N. G. Well, I don’t know. It certainly did well for us. Pokryshkin fought in it; doesn’t that say something? [Aleksandr Pokryshkin was the number 2 Soviet ace at the end of the war and flew a P-39 from late 1942 to the war’s end – J.G.]
It seems that everything depends on what you wanted out of it. Either you flew it in such a manner as to shoot down Messers and Fokkers, or you flew it in a way that guaranteed 120 hours of engine life."
There are other highly respected pilots who have said the P-39 was an excellent fighter, such as Chuck Yeager. And he is one who definately has strong opinions about planes.
The P-63 Kingcobra was an excellent performer. It had 1800 HP, laminar flow wings, and was considered to be on par with the P-51.
Astronaut Frank Borman owns one. Do you think he'd buy a poor performer? See hyperlink below
Now to your question about why add planes that no one would fly.
1) The P-39 is an absolute must have for the historical scenarios. It and the P-40 carried the flag for the USAAF for the first two years of the war.
If AHII has a time cycle to it, so that the war progresses over a time period, the P-39 will again be a must have for 1941 - 42.
In the MA it will be as much of a hanger queen as the P-40 is, but it will surely get flown. It may possibly find a niche in the MA as a low altitude ground attack fighter.
2) The P-63 will be able to fly and fight with any of the late war planes. It would help fill the lack of Soviet Air force planeset.
Frank Borman's P-63 Kingcobra [Aleksandr Pokryshkin was the number 2 Soviet ace at the end of the war and flew a P-39 from late 1942 to the war’s end – J.G.] 
