Valid point, although i rather not look at clubs like Manchester United. If you look at the most succesful clubs in the last decade, they all had players that wore the identity of the club they were playing for. And as i said, not necessarily leaders, but players you think of when you think about a certain club in a certain period. If you look at clubs in their prime, they all had these kind of players, and it definitely doesn't have to be players that been at the club since they were young. It might help, but some players adapt easier, and have a different mentality than others.
Lahm, Ribery, Muller, Schweinsteiger, Robben, Neuer
Iniesta, Xavi, Puyol, Dani Alves, Messi, Villa, Pique
Cesar, Zanetti, Maicon, Sneijder, Cambiasso, Milito, Eto'o
Kroos, Marcelo, Ramos, Benzema, Ronaldo, Modric