Mike, for me his lack of athleticism does hurt us, especially when we are vertically challenged on the front line to begin with. For me, though, its lack of hustle at times on defense and on the boards as well as questionable decisions he makes with shot selection on offense. Last year's team did a great job with ball movement and player movement to get open shots. When Miller would come in the game, it seemed that the ball movement would stop and he'd force way too many shots.
You are right though, we need an athlete or two who are energy guys who will play hard defense, defend the rim and rebound. They don't necessarily need to be able to score although that would be nice.
I should note he has the second highest assist average on the team.