I am not a pilot, but I am a Chartered Engineer, Chartered Statistician, a Chartered IT Professional, a European Engineer, and a Fellow of the Royal Statistical Society, with a Doctorate in Operational Research and Mathematical Statistics.
Not all natural distributions are Normal. However, very many are, because of the Central Limit Theorem. In essence, if a physical measurement is the sum of smaller figures, it is very likely to be Normal. That's why heights of people are approximately Normal, IQs are roughly Normal, etc.
It would be very surprising if the performance of pilots differed much from a Normal distribution.
A Normal (or Gaussian) Distribution is entirely described by its mean and variance. So, unless the distribution of performance of pilots is very unusual (such as a Laplace Distribution), the only relevant features of the distribution of pilot performance will be the mean (or average) and the variance (which determines how many are in the "tails" and how long the "tails" are).