Nope, do not agree with your definition, especially the reference to "stamina and overall fitness." Neither one makes you more or less athletic. By your definition all marathon runners are athletic, which we all know is not true. And, to your first point there is nothing "traditional" about the definition of athleticism, because it's all based on conjecture, or various bias opinions. You can't develop it, can't take a pill to improve it, or lose it, if you stop exercising, it does not go away. The amazing thing about an athlete who exhibits exceptional abilities in one sport, yet fails miserably in another, is that his athleticism does not change, but his performance level does. In other words, if a person excels in basketball, is athletic, that doesn't necessarily mean you will excel in baseball. Ask MJ. Because, there are other factors that come into play, like fundamentals, experience, hand/eye coordination, genetics, etc.
As well as great athletes don't always translate to performance superiority. For this example, all we have to look to is the "Fab 5" of the Michigan Basketball team a few years back. They all were extremely athletic. And, thought they succeeded to change our perspective on many things that is basketball, they were still beat(twice), by teams that did not have the overall athleticism that they exhibited. Fundamentals, knowledge of the game, and teamwork + coaching, can overcome a deficiency in overall athleticism.
Anyway, that's the way I see it. Just IMHO....