Last year Jason was at times an extremely effective defender against some of the league's best. He caused Love problems, and was a primary reason Anthony Davis struggled against us. He had a big number (-3.4 per 100 possessions) on/off as well. Cuz was at -3.7. You can't always trust on/off stats, but they seemed to reflect what we were seeing in this case. Cuz wasn't the only guy to noticeably improve with real defensive coaching.
We were actually pretty good at playing man to man defense last season from top to bottom. Even the all hated one, IT, had some of the best on-ball pressure in the league. Not too many guys took Cuz to school in the post in 1v1 scenarios.
The issue comes instantly with rotations. Nobody on the team had/has any idea how to rotate on defense. We got destroyed by a single pick being set on the ball-handler. That's where a Mbah a Moute, as old and decript as his knees are, was such a big help I think to the team defense. He was a real defensive leader and was always in the right spot on his defensive rotations and that carried over a bit to everyone else.