The Pony is just an all around darn good freaking airplane. You have indicated it doesn't particularly shine is one area (i disagree here btw, how about e retention or dive) but is better then average in most.
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This is just plain wrong. Please learn your AH planes before you comment on them.
The fact is, for a fighter role, the 51 is probably the worst late war rides. The k4, la7, d9, 152 are all late war rides that are clearly superior to the 51D overall.
The K4 is an uber fighter, much better than the 51, yet its ENY is much higher. It out turns, climbs, accelerates, rolls about the same, out guns the 51 yet its ENY is significantly higher. I can only assume that ord carrying ability has something to do with ENY, otherwise it doesn't make much sense to me.
For me personally, I don't care about ENY because I like to fight the horde, it's fun. I have an abundance of perks so farming is of no import to me.
RTholmes, the other late war rides are no more difficult to get/land kills in, with the exception of endurance, especially la7 vs pwny. As for endurance though, how much fun would it be to cruise around and get 2 or 3 kills an hours..... zzzzzzzzz.

Clearly the 51D is inferior to it's contemporaries, in a fighter role.