Hmm....
If you were to drop the ENY of the K4 to 10 or 15, you would have to do the same with the F4U-1A as its another perfect example of a plane with a slight learning curve but once you know it you can be REALLY good. I don't know of many planes in this game that can float 500ft above the ground at 80 mph but the 1A can do it. Not to mention the crazy, crazy ACM you can pull out of that bird in a pinch. Yet it's 20 ENY.
I guess what I'm getting at is there seems to be a few planes that are "over ENYed", not just he k4.