It's not like Oliver is some blind gamble, his talent has been standout for quite a while. If the club is willing to nurture and develop him, then it's almost guaranteed that he'll sustain his performances and become a great player barring injury. I mean being "proven" doesn't always have to be a prerequisite for a transfer, why not get a player to his best after buying and developing him instead of waiting for another club to showcase his ability and then jack up their price significantly before the purchase. He'll be 21 but his position doesn't have as much pressure as goalscorers or forwards, he'll be a great squad player even at that age. Besides we're going to shift around after Xavi retires anyway, it's not like the burden completely drops onto Oliver's shoulders just like that. As he gets better, he'll take on a more influential role, it won't be forced onto him the moment Xavi is gone.
