Actually, I see two very valid sides to this argument...
One is that this is a game, not a technical study by a college for publishing in a journal. I'm sure you could take all of the factors mentioned and create a very valid rating matrix of every plane in the game list. But that is not the point of AH2, and it needs to be remembered that this is still a game...where it is more FUN to fly certain kick-butt, high-powered, heavily-armed planes at really high speeds for some people, and more fun to others to have a very tactile experience with the airplane, more like a game of chess would be, with wit and strategy factoring in (thus the actual plane choice makes less of a difference). In this respect, using "how many times xyz plane is picked" as a factor for ENY does make sense. If it is more likely that people will be flying a certain plane, more of them in the air at any given time, etc. etc.
On the other hand, all of the arguments regarding the lack of consistency with "real" war-time statistics does bear consideration. I just think it has less value than the first argument above. I also think that, while this comparison of significant airplane features would provide a consistent ENY value rating for all the planes and new planes, I think that most pilots place less emphasis on what the actual ENY value of the plane is.
I don't know how many times, can't count, I've been blasted out of the air by a well-placed shot from a HurrC. Then again, I've also pounced many of them in faster planes because they couldn't get out of their own way... So I think the ENY rating has less importance and the marriage of pilot skill/plane choice really has a lot to do with it. I hate Hogs, because you can't see out the back of them...but then I get killed by them all the time too...so the ENY of my plane doesn't help me, and my dislike for the other plane has nothing to do with the ENY of that plane.
Great topic, btw.