No, we can NOT say that.
The guy traded three-pointers over and over again with Kevin Durant in the H.O.R.S.E. contest at NBA All-Star Weekend 2010, and proved quite easily that he can shoot the ball, (granted that was just for "fun").
As far as getting it to go with regularity during games, (along with foul-shots), that's something that will come over time.
Please, never say never ... I've seen way too many people in this life swallow their words over things much more unlikely.
This kid is incredibly talented, and was a huge scorer in high school and college ... let's give him the benefit of the doubt, and be thankful for the gifts he's already sharing with this team!