It was a real piece of crap that saw high attrition rates in every theater employed by the USAF. Just as well that the Russians got some use out of it. Better than nothing, for sure.
Supposedly they had been designed with the turbocharged version of the Allison engine in mind, and performed very well when they had it.
Not really, in Russian service it was extremely successful. You have an uninformed opinion. Five of the 10 highest scoring Soviet aces logged the majority of their kills in P-39s. Grigoriy Rechkalov scored 44 victories in Airacobras. Pokryshkin scored 47 of his 59 victories in P-39s, making him the highest scoring P-39 fighter pilot of any nation, and the highest scoring Allied fighter pilot using an American fighter.
The high attrition rates in USAF were due to early war poor tactics, meeting Zeros in maneuvering dogfights that no other fighter on earth could turn with, and in Europe we operated at high altitudes that it could not function at.
It was a plane constructed around a cannon.
Something like:
Don't give me a P39
With an engine mounted behind
It'll tumble and roll,
and dig a big hole –
don't give me a P-39.