Our bigs are slow, non-athletic, soft, slow reacting. Horford, KO, Amir... We have no quick footed, long, players that get off the floor quickly to come out of the weeds to defend drivers in the paint, and slashers.
Kelly is abused something fierce, being at times thrown to the floor, always looking for the refs to stick up for him. Horford is a gentleman, Amir is running on fumes. Jerebko is a finesse player.
We're undersized everywhere, but especially in the backcourt. Our leading scorer is a 5-9" PG, that we need on the floor for us to score. He's defending against the best 6-4" players in the world. Is he taken advantage of? You bet he is. Like Scal said, he plays as good a D, as you can expect from a 5-9" player to play. In other words...deal with it, he'll alway be a defensive liability.
The formula for success on this team is not right. We may have to take a step back, to take a few steps forward.