Too extreme at both ends. KJ's handle doesn't stink, nor is it "nasty." It is a liability as judged against NBA skill sets. His left hand is particularly weak, even relative to BE talent. He is great at getting to the hoop using his right hand, and this tends to mask his weakness. I don't see many here mention that, but watch for it in games. I think Buzz even talked about the need to limit him to one direction in his presser. You can bet that Pitino and Calhoun will over play his right as well.
"Handle" also encompasses his tendency to get out of control with the ball.