I think that's it too. Really that simple. As he's slowly gotten better about that, his minutes have slowly gone up. Now maybe a little more improvement and experience (quit swiping at balls in the first quarter Cuz), and a little more respect from the refs as the narrative changes, and he can squeeze out another 5-6 min a game.
P.S. I do think fatigue is a factor and he will have to pace himself. But that's completely normal for franchise bigs too. I can remember Shaq huffing and puffing, and Patrick Ewing dripping sweat like he was in a sauna every game. But the fact of the matter is that unless you are extraordinarily blessed with a once in a lifetime frontcourt, even a tired Shaq or Ewing of Cousins is going to be better than a fresh whoever his replacement is. Just have to avoid the tired fouls.
I've always found it interesting how players like Cousins, Shaq or just about any big man is held to the same standard as a Chris Paul or a James Hardin as far as energy and stamina are involved. Lets see, a player like Cousins, has to drag his 270 pounds up and down the court and when he gets there, he has to sumo wrestle with another 6'11"/7ft giant to acquire, and then maintain position in the post, and then fight for position under the basket, in an effort to get the rebound. Meanwhile, while this is occurring, the guards of the world prance around on the perimeter, unimpeded, and are the first to leak out toward the other basket after the shot goes up. And the result is, the Cousins of the world get criticized for being the last one's down the floor. Really! Duh?
Now I'm not saying that the big men in the NBA shouldn't be held to a certain standard. Of course they should. But I think that fans should realize that the game a big man plays in the NBA is a different one than the 195 pound guards play, and they shouldn't be compared. As far Cousins, when he came into the league, it was difficult to keep him on the floor for 28 minutes a game. That was due to some extent to being in foul trouble, but mostly to his lack of stamina. When your tired, your feet don't move, and as a result you tend to defend with your hands, and that adds up to more fouls. One begets the other. Last season he averaged just over 32 minutes a game. A four minute improvement on his first year. Why? Because he was in better shape, and by watching him in the world championships, I'd say he's looks to be in the best shape of his life. As a result, I expect that his minutes will go up.
Defense is two fold. It's about first stopping the ball, and second, defending the ball. So, if your a smart defender, you should actually use less energy than if your a dumb defender. It's like skiing or golf. The better you get at it, the easier it is. Now I know some will disagree with me, but it's easier to be in the right place at the right time and stop the penetration, than it is to chase the ball after allowing penetration. Plus, if done correctly, you make your teammates job easier as well. But that's another discussion.