Actually he's kind of stubby -- really NOT built to be lockdown. Can't disrupt with alligator arms (actually closer to average length than below average). Also a better straight line run/jumper than he is laterally, which is where defense is really played. He can catch guys from behind, but guys get aroudn him a lot.
But obviously he could be better. Not sure that is really the issue though. Afflalo has been a good defender in his career. Temple is a good defender today. Ben could be a good defender and not stand out on that end. I do think the bonehead mistakes and inconsistency may have knocked him back though, while we are trying to get things together under the pressure of a play every night schedule.
Could see him get time tonight just because of fatigue. Could see him emerge later in the season after the vets have helped establish an identity. Its just hard to form up a team identity when you've got kids still trying to find their own identity in the mix. Willie has suffered from the same problem. If we're a stable winning team with a stable wining culture, then you can afford to have a kid or two on the fringes figuring things out, being inconsistent, etc. and the rest of the team goes on its way. but when you are still trying to forge that team identity, its a lot easier if you do it on the backs of guys who already have their own stuff sorted out.