I'm not sure what you were watching. His defense was quite good guarding Simmons all night, especially in the post. 18 points on 16 shots is CJ like efficiency.
We'll see what you think by the end of the season. He's not efficient at all. Last two years TS% .463 and .497 is awful and -2.6 career offensive BPM. By contrast Harkless was .595 and .547 and could play defense. CJ is not that efficient -- doesn't get fouled enough. Still at .500 and .553 past two years.