Datome is an OK player but not for the NBA. First, as you say, his D is weak. Second, he is OK in many aspects of his offensive game but he excels in none, he has no 'killer move'. Even in Europe, he was never a great scorer. Third, he is already 27 yo so he can hardly be classified as a talent. Last, he lacks explosiveness and physical strength, which makes it very hard for him to compete against other forwards in the NBA.
Since he is an expiring contract he can hardly be used in trade.