I'm not saying he was handled correctly, but I'm not sure what you think the team did wrong.
Let's see. The team had dedicated development coaches for Bennett, and those guys were the only coaches that survived the off season. The team encouraged him to get his own cook to adjust his diet. They had him bring family with him to Cleveland so he wasn't left alone in a strange town. The guy wasn't dropped off at the bus stop ...
Now Bennett had adversity. He had the shoulder surgery 6 months before training camp. Bennett also had the weight, apnea, and asthma issues. Hard to blame those things to mishandling though. Those were just red flags on his draft report that the team though they could work though.
The team was not a great place to be last year. The training camp was rumored to be pretty disorganized. The locker room was a mess during the season and filled with drama magnets. The team sucked and lacked structure, but that just didn't affect Bennett. Some of the young guys like Dellavedova, Sims, and even Waiters seemed to work though the situation OK. They were a little older, but not that much.
Bennett did look like he was starting to turn the corner last February but he came down with knee issues shortly after he seemed to start putting things together which was a shame.
If only there was a way to transplant some of Waiters excess self confidence into Bennett, they both might be better players for it.