Well he is 15 in PER for rookies
I mean it's not good but not as bad as painted
Almost like saying Ayton sucks
He had three or four fantastic games early on, which boosted that number. He has been garbage for well over a month now, and the team's play has slipped noticeably every time he is on the court. Also, a lot of other rookies have far further to go in their development, so PER is a misleading stat here. A lot of younger rookies are barely getting playing time as they learn how to play basketball.
His defense is as bad as Saric's, he can't rebound, he can't put the ball on the floor, he can't pass, he is ridiculously passive, and he is remarkably slow and unathletic. If he isn't hitting the spot-up jumper, he brings absolutely nothing to the table.
And it's not like he is young and inexperienced, such that there is room for development. This is who he is.
Basically, with the stationary jump shot instead of passing ability, Cam is the one-dimensional bust with no ability to develop further that Kendall Marshall was.