If you are meant to be there, you'll get there. Meaning there are a number of players that would have "made It" regardless of where they played, they just had to play, period. Those players possess special talents, just as most that make it do (ex Albert Pujols, Mike Trout, Bo Jackson, Bryce Harper and Alanzo Cane). All can do what is deemed the toughest thing in sports and that is HIT.
An overwhelming majority of MLB players have a special talent and todays baseball is more specialized than ever. Pitchers, throwing to one batter for a matchup. Jerrod Dyson the baserunner, and so on.
If a young player wants to play one sport, fine! If the player wants to play multiple sports, great! I believe it's largely in the gene's, but who's to say a special talent doesn't come screaming out nowhere.
For most, playing baseball is to play baseball, as it should be. For a very small minority that dream continues beyond HS, in which there are an abundant amount of opportunities to do so.
As for the amount of games........ I have first hand account of , back in the day, when a young pitcher only played 25 games a year. However, he would guest on other teams frequently and regularly toss double headers. I was told it only took him 25 games a year to "make it"(LOL) and of course when my F-I-L told me this story and tried to relate this to his grandson playing a scheduled 55 games at 15 yrs old, that happens to only throw in a closer role. I quickly done the math and concluded my son probably throws half the innings in comparison to the pitcher from the '70's. That pitcher? '84 NL CY winner, the "Red Baron". I only tell this because I believe "players" find a way to play the game, albeit in the backyard with a tennis ball or playing caps.
Players simply find a way in spite of anything you do for them.