Sorry, lads/lasses. But having been involved in player development for nigh on 20 years, having worked with youth players who went on to be professionals and internationals in a few cases, I can say with a good measure of certainty, that most here have a really idealised and incorrect view of elite youth development. Truly top class players aren't held back. They are, in fact, promoted quite readily. The sad truth is that most players in the academy level will only ever have good and steady careers. Some will have great careers but will be "water-carriers" for the teams they end up playing for (not unskilled, but not the standout player in a top team, either). And then a small percentage will become all-time greats. And a further percentage will drop out of the game altogether, or become coaches instead of players.
But for anyone to sit here and say that just because youth academy players aren't getting their chance at City, or Chelsea, or whoever, that they are not ever going to reach their full potential, and that we won't know a Messi unless they are given a run of games, is naive at best. We ALWAYS know that player. They ALWAYS stand out. Whether they become a great is largely up to their professionalism and dedication and ability to turn talent into consistency (see the aforementioned Robinho, but also Balotelli for a more polar extreme example). But they were never "hidden" behind 2 or 3 inferior, but senior, players at their clubs. They were obvious talents. Barca didn't sign Messi up on a napkin in Argentina on the flip of a coin. They saw what he could become with the right guidance. They didn't take all of his youth team-mates as well, just in case it was the coaching that made Messi great at that age. They took Messi. Here is a good article about Barca signing Messi. When you see that player, you know. You don't know how far they'll go, but you know that they have the tools to go far if they apply themselves:
https://www.theguardian.com/football/blog/2014/oct/15/lionel-messi-barcelona-decadeIt's all relative. Academy players in general stand out from their local peers, and that's why they become Academy players. Then in the Academy, they stand out from their team-mates, so they get to play up an age when allowed. Then they stand out from their select peers who get to play up an age, and they train with the first team squad. Then they stand out from the squad players, so they get put on the bench. Then they stand out from the bench players, so they get a start. Then they stand out from the starters, so they get a run. Then they stand out from the league, and they become a transfer target. Then they stand out from the opposition, and they become a great.
Everyone's progress is measured on that ladder just there, and everyone has an upper limit. It's not like players go home and do nothing from game to game, and then just turn up an hour before kick-off and the manager has to guess who is capable of what. They are constantly being informed by their staff of the progress of the Academy players in training, and if anyone stands out, they will be urged to have a look at them, and if they like what they see, they have them work with the first team, and if they stand out in first team training, they get minutes. That's the process. No manager is going to come across a top class Academy player, watch them turn the starters inside out (or mark them out of a training game), and then say "You know what? I don't need that player. Keep him with the other kids". My mind boggles that anyone would think it was different than that.