Not sure if it's a zero work ethic, necessarily, but he definitely seems like a kid that lacks drive to be more than he just naturally is. A kid who has likely relied solely on his talent to this point in his career. That will get you so far, but at some point, at the highest levels, the talent margin is mostly razor-thin. At some point, you have to gain advantages elsewhere like your diet, the time you spend in the gym perfecting your form/shot, the time you spend on conditioning, in the weight room, film study, etc. Those things are what separate the elite players from the good players. If he can't learn to want to do all those small things, then as the talent margin narrows, he will begin to fade because he can't rely solely on his talent any longer.
These are the kinds of things that Rick Barnes can help him with the most, but not if he thinks he's a one-and-done player. Those habits and mindset changes won't occur in one 8-month period. He would need to stick around for at least two years to reap the benefits of that kind of coaching and motivational push.
