I doubt Cousins will be a top 10 shotblocker in the NBA, but I see no reason why he cant average a block+ a game. I mean, Spencer Hawes was #27 in block shots last year among centers, with 1.15 bpg. Add in the fact that Cousins will be much better at keeping guys out of the paint with his strength .. Im not too worried about him on D.
Especially if he is paired with a guy like Dalembert or Whiteside. Both guys are MUCH better weakside blockers than man defenders, so long as Cousins can keep guys from backing him down, the help defender should have enough time to slide over and block shots. This is something Donte Greene was able to do last season too.
One thing to remember about summer league is that, like college, most of the damage is done by guards. I mean .. how many chances did Cousins REALLY get to block a shot? Monroe got the ball in the post what .. like 5 or 6 times all game? The pistons only scored 68 points. Whiteside was getting all of the weakside blocks available anyways.
Not to mention a charge, something Cousins wasnt afraid to go for on multiple occasions, is MUCH better than a blocked shot. You get possession AND the player gets a foul. Im not sure what a good number for 'charges per game' is but if Cousins can average about 1 charge and 1 block per game, and play solid positional defense .. im fine with that.
All that being said, Cousins just isnt the best athlete. He has good quick feet, but he's not the crazy leaper that Dwight Howard or Hassan Whiteside is. I dont see how he can ever be 'that guy' but like I said 100 times in this post, I think his defense will be fine.