Hope Martinez made him did a couple extra hours of passing drills. There are loads of players who can keep their head down and dribble very quickly with the ball. Players that get their heads up are the ones with the potential to become world class.
I don't think the comparisons to Coleman are appropriate. Earlier in his career his final ball needed work, but he would at least deliver a final ball. A great example is when he assisted Cahill's goal in the 2-0 derby. Coleman ran with his head down and only briefly glanced up before sending in a ball, Cahill was in the right spot because he was watching Coleman's run very carefully and knew where to go. But even though Coleman didn't pick out his cross carefully, he at least knew to cross. Only more recently has Coleman started making those cuts inside, trying to take it straight to goal, and even then he frequently will lay the ball off for teammates very intelligently.
Duelofeu's problem isn't that he can't pick out a pass, it's that he doesn't even look for the pass until he's just about lost possession. Also stopping the ball for 5 seconds in the box and doing a few stepovers before doing **** all with the ball doesn't make you world class, it just makes you look like a tit.