I'm almost positive that you are talking about Pargo who is an NBA talent for sure. Pargo played mostly at the point and brought the ball up last year so that Raivio could work off the ball and get more shots. On defense they play zone quite a bit and if they are man-to-man Raivio would usually guard the other teams PG.
You are right, DR has to work on his defense for sure. However, I don't think its a disqualifier for him and I believe if he put as much work into it as he does his shooting he could definitely become a solid defender because its not like he's slow and he is the same size as most of Atlanta's other PGs.
I hope Raivio gets a good amount of playing time in summer league and that he shows his best out there.