How efficient are pro sports at producing superstars?

[Sooga]

I wasn't sure how else to title this post, but basically what I'm wondering is, given a player with superstar-caliber natural abilities/physical gifts (e.g. Kobe, Pujols, Randy Moss), how often do these players actually turn into superstars in their respective pro leagues?

In other words, how many Babe Ruths have come and gone from the league because they stayed on the bad side of variance a month too long? How many Michael Jordans have we missed out on because he didn't get enough playing time/was in the wrong situation? I don't doubt for a second that the superstars we have in every league truly are among the best in the world, but how many others should be there too?

On a related vein, do you think true superduperstar athletes are born, or made? Like, take an average Joe Schmoe, but let's make him 6'5" to make things a little easier. Assuming he did nothing but train starting as a toddler, how often would he make it as a pro basketballer/footballer/baseballer?