I believe that Legion stat about 50% of the MLB players having played Legion. At one time it might have been higher and it will continue to drop because things have changed.
Problem is that most all of the younger MLB players did not play Legion. Most all the top draft picks over the past 5 - 10 years have played travel/club baseball. For every Legion player you can name drafted in the top 5 rounds, I will give you 10 who played elsewhere. In fact, I will give you 25 names.
It's odd that so many don't (or won't) understand this. Understand that most HS draft picks come from 3 or 4 states. Illinois is a great baseball state, but it is not among those 3 or 4 best states. Also, if you look at the rosters of the top college teams from th top conferences, you will see that nearly every player came out of travel/club baseball.
There really is no argument regarding any of this... It is a fact! As always there will be a few exceptions.
BTW, I have nothing against Legion Baseball. I grew up with it and my kids played Legion. One son would be among those 50% that played in the Major Leagues. Things have changed in a very big way since then! But believe what you want!