Top clubs shouldn't be hoarding talent to the extent they do anyway. Alli came through at MK Dons or Stones at Barnsley and they got a good education, game time at a young age and then got big moves from there when they were ready to play. All top clubs need to stockpile all this young talent to compete with each other though.
Real Madrid's approach does work at times. They get a player like Asnesio or Carvahal in at a young age, loan him for a couple of seasons in La Liga or another big league and then when he's got the experience and is physically developed he's ready for their first team squad and they keep a place in the squad for him so he gets the games. Real will prioritise Spanish players though (hence wanting Diaz) so someone like Odegaard will have to be amazing on loan. Chelsea have tried this approach but when the players come back off loan they don't get the game time, get frustrated and want to leave. The best approach is loans but it's keeping players content on long contracts while they get the experience elsewhere. The likes of Sancho and Diaz etc are less likely to show the patience if they don't see a path to the first team and a place in the squad available to them. The only places in our squad are left back, maybe CM and striker if the likes of Yaya and Delph go.
It's very rare a player will make it through at a top club from the youth team and it'll usually be because an opportunity comes up. Rashford got one at United because no other strikers were fit and he came in, scored and took his chance. Harry Kane got his chance because of how much of a flop Soldado was.
But you look at LIverpool giving Alexander Arnold games, an excellent prospect, but he was ripped to shreds by City last week because he's a kid and inexperienced. It's difficult to just throw them in without that happening. It's also rare that a young player will be that good that he'll improve the team when you have a star studded squad. Fans would moan if we had a youngster in who struggled like that in a game, or moan if we sold, say, Sterling or Sane to open up a squad place for Sancho or Diaz to play. Look at that meltdown when it was suggested Sterling would make way for Sanchez.