They're certainly not all world class, look at Busquets as you say, and how Bojan has stalled, I'm not massively impressed by Jeffren etc etc. They pick players for roles who they think can develope into world class in their position. It's easier to bed a player in when they are playing in the same system and role since they are 14 years old. Because they win so often they can also afford to throw them in now and again, hardly any young players are going to play at Juve in such a struggling side.