The important thing, is that much like Rondo he is only 24years old and is already a pretty good NBA player. However he has much to learn but with his athleticism and current skill set I think that he can definitely get to averaging 15-20points within the celtics system once the big 3 retire..
looking from a long-term perspective, Danny made a good move as you have 2 solid young players that you can begin to build upon to keep the team a championship contender well after the big 3 are gone