Yeah, kids should just play sports. In my home town, there was a kid (not my age) who dominated in basketball in middle school, then high school (he was also quarterback, was named the state's best football and basketball player), then dominated at the local university in basketball, then went to the NBA. Didn't dominate, but did decent. Now he's back in town as the head coach of the university basketball team. That's what elite looks like. It was pretty obvious that the kid was awesome from the beginning. You don't need a genetic test to tell you about that potential. It also doesn't mean that everybody else on the middle school team should quit. Or even care. They liked playing basketball. I think it's pretty obvious that most of us don't have elite genetics and that doesn't mean we should stop trying to do the best we can with what we've got.
Okay, one exception is if both of your parents are 5 ft tall. You probably won't get far in basketball or have much fun (or playing time) once everybody else gets a growth spurt.