But dude, has any of these teams slowly introduced a young player to their squad and let them develop at their own pace? I don't think there's any recently.
Any youngster induced to their squads recently had to deliver instantly, player like Pedri, Fati, TAA, Davies... are simply too good and age is simply a number to them. Instead, you should compare Casadei with Riqui Puig, Pulisic or Kubo who are now stuck in the limbo of being talented yet underdeveloped. For these players, the argument has always been they should have left when they could.