So called special forces have been around since WWII. This is not to be confused with what were called "elite troops," and even that had two definitions. One was socially elite, like units called guards, the other militarily elite, like most paratroopers or marines. That's not quite what special forces are (not to be confused with "special services").
Not everyone is a believer in special forces, as the term is usually used. They consume a high proportion of resources, although they may accomplish a lot. They sometimes have a way of becoming private armies, too. And they can only do so much. A negative aspect of such organizations, if in fact they do result in the concentration of the better soldiers, is decreasing the average overall quality or all the other units.
However, you are correct in that only a relatively small percentage of soldiers cause casualties to the enemy, or supposedly so. That's true whether they are riflemen or fighter pilots. I doubt training enters into the matter. I'd say it was a combination of two other things. First, willingness to do harm to the enemy, and second, natural ability. You have to face the fact that people have different abilities. There's no way to train people to see better, be taller (or shorter) and so on. I have poor eyesight. No amount of training will change that. Others are gifted with better than average eyesight and that's an advantage for flyers and it usually helps when you're shooting.
And speaking of Middle Easterners, there was a photo of a Syrian family on the front page of yesterday's Washington Post. The kids had red hair.