The P-39 would make a good B-n-Z plane, with that listed Dive speed(620 mph.) What made the cannon worse than the 20mm hispano armed P-400, though, was it's tendency to jam in ACM's. Now, keep in mind, that since several other guns would do this(The 20mm Gondola guns on the 109's were known to jam, I've read) Then we would have to ask ourselves if it would in AH, Where NO gun jams were modeled.
Also, the P-39's historical record as a fighter in the Pacific could be attributed to pilot training and tactics, which were being developed and did'nt really exceed that of Japan until about 1943.
I would also add, that if the Russians produced a 59 kill ace(Alexandyr Pokryshin) in the P-39, then maybe the U.S. was doing something wrong?
And finally, I might add, Spin recovery is a chore in alotta planes, which are optimised for High-speed High alt flight.(A Pitts will recover from a Flat spin inna Heartbeat...But it's not designed to fly 350-450mph. at 20-30k, either.)