I think that it is quite sad only to be intersted by performances, even if it is important...
For your american planes for example, I really prefer your P-40 flown by flying tigers pilots than P-51 in Europe... it's quite easy to chose the best plane. In a simulation I aslo like using planes that weren't the best about performances but that won many victories with great pilots, it's an intersting challenge, more intersting on my mind than destroying noobs in a Corsair. If the only thing important in AH was speed and power there would not be other aircrafts than 109, P51, Ki 84, P47 or Corsair...
I still think that a squadron with D-520 could easely be dangerous for your great planes.
D-520 was not as obsolete as other french planes, I think speed performances weren't so bad, and fire power was intersting. Dewoitine Pilotes managed to destroy many ennemy aircrafts, even if they had not many time, and they didn't lose many of their planes.
Perhaps that's not the way of thinking of everyone, I am above all interested by history, I prefer flying a spanish Polikarpov I-16 against a 109 than a P-51 against japanese zero or fw190.