IAR 80 was an interesting bird I never got to research completely, but from what I do know - Its a typical early war bird. Lacks any heavy guns (6x light machine guns) range was limited, speed was decent at 330 at alt.
When you look at the D.520 - it was simply a state of the art design, 345mph at alt, with pair of hispano guns, fact is D.520 fought in 1940, while IAR 80a was end of 1941+.
D.520 had to fight the best the Germans had to offer the 109E, while the IAR 80a went against whatever flying junk the russians could put up (and pilot skill wise).
It might of been in service till 1944 for good reason, it had absolutely no competition in equal terms... Frankly even if the IAR 80c gets added, it was no way near in performance to any american plane flying over romania in 44, other then turn radius.
I only cast my vote on the D.520, because I have more solid information on it. Honestly I joke much about the french, but this bird was actually pretty wonderful even if it was a footnote just as the IAR 80 was.