night Deron Williams had his way with Neto in the 4th quarter backing him down and that's why the Mavs came back and Neto had to take a seat. Exum was an excellent rookie defender. The defense gets him on the court and immediately improves the team, and then as his offense gets better, so will the team.
Remember, he really only needs to be the 4th or 5th scoring option out there because Hood/Hayward/Favors are great scorers.
So yes, I agree, he needs to be better on offense. But let's not forget how good he was on defense and that makes him useful here and now while his offense grows.