What's to say he's not going to improve on defense also? You say he worries more about his shots than making others better, are you so sure he is always going to be like this?
Guy is 21 man, it's not a good thing he left the Warriors.
It may be good for you since you are a JRich fan, but for the team I don't believe that it's a positive. The Warriors will miss the hell outta Arenas next season.