Its no more rare then the Chog or the 152,if your that worried about balance just perk it silly 
Besides, some of us prefer american iron over plywood brit kites 
Not worried about balance so much as the historically significant aircraft going unused while the historically insignificant aircraft sees a lot of use.
I don't think the F4U-1C was a great idea to add either, but look how well that turned out.
Nation favoritism is just silly. Particularly when it is about using a bomber as a fighter.