Developng youngsters is a double-edged sword: if they succeed, it's great and sweet, but if they fail to live up to the expectations you have wasted 5 years and start the next rebuilding from a worse position. It's highly risky: you might end up with another class of 92 or with another 5 years without a title.
The only thing I say to this is that it is exactly the same with bought players. There is a risk. We have had numerous bought players in the last 20 years which are no better than others in our youth system. Yet because we paid big fees they automatically get chances others don't, get given the benefit of the doubt more, and tend to play more games.
You don't know any of this in advance, so you just have to have a plan/philosophy/process and trust in it.
I reckon we made mistakes with the likes of Buttner, Diouf, Bebe, Obertan, Bellion, Darmian, Rojo, Blanc, Ricardo, Djemba, Kleberson, Miller, Manucho, Tosic, Powell, Valdes, Depay, Schneiderlin, Schweinsteiger, Grant, Fred...
We could have played a dozen kids like Higginbotham, Shawcross, Keane, Drinkwater, Simpson, Rossi, Gomes and others and not necessarily weaken the team.
As always it's about balance, but there is nothing to suggest those players would have been worse.