His defense is overrated as too... yes, he's long, and his defense can be summed up as reaching for steals (which granted, he does relatively well).
There's no lateral quickness, no physical tools to bang up with anybody, he isn't stopping anybody one on one, poor footwork to stay in front of his guy, and at a severe disadvantage on the athletic department on a league full of athletic freaks.
Players like him are dime a dozen in this league. The Spurs are better served using that roster spot signing some promising kid on a rookie deal and develop him. Save time and money.