Ok, so Januzaj and Pereira then. The 90-minute rule has made it difficult for English teams to do what you described.
And the obvious benefit of having the academy produce youngsters for all tiers of English football is that the youngsters see that most of the ones who come through our academy is able to make a living from playing football. No one would bother to choose us over another club if our track record was terrible, but the fact of the matter is that Manchester United has been producing an insane amount of professional footballers for the English league system. It might not be an instant "fix" for our first team, but the academy isnt supposed to be anything of that sort either.
We've been spoilt in the past with great players coming through our youth system, but the pressure was much less in those days and the consequenses of losing a game is much bigger now due to the competition and prize money. We can only afford those let the very best of our youth system have a go, and it might not be something we like, but due to the competetivness of the league, it's something we have to get used to. Barca and Real amongst others have been able to give their youngsters plenty more games than we can afford, simply because the competition is worse. Their U21s are also allowed to play in the league-system, which means that they will be matched against tougher opposition on a regular basis and it'll allow better development as well. I would say it's alot more complex than what you are making it out to be.