There are too many factors that the math cannot predict. Which is why there is playtesting. And why Attack Wing is having severe issues with their way too simple formula and Wizkids "playtesting".
I will say, you really should stop laying claims on what theoretical stat lines should cost. Anyone with a lick of experience in actually playing the game could tell you a 3/3/3/3 TIE Fighter at 24 pts would break the game.
As for the X-wing, I think the answer is fairly obvious. The B-wing fills a very similar role. X-wing are moving more toward the uniques, and that isn't necessarily a bad thing or a sign of them being inefficient.
