He's a quality player but he can't make things happen, like playing as central midfielder he can't control the midfield. He's way too slow for tight areas and his decisioning, passing are still questionable. What i personally think is that he will never find a starting place in the team. Busquets has many years in fron of him and Song as i said won't make it as central midfielder. If he wants to stay a rotation player he could stay but if he wants a starting place he should leave.