He was not without issues last year either. We all remember the switching 1-5 on everything, and how poor their defense was. It took him too long to change it up, imo, as it was obviously not working. After finally stopping the switching, their defense improved overnight, and drastically. There was a lot of times of stagnant offense, no one moving off-ball. A lot of 1-1 and two-man game, with the others standing on the 3-pt watching. These issues were covered up a lot by players making tough shots. There were a lot of times in which they were not put into position to get good shots, they had to take bad shots - they just made them more often than they are making the bad shots this year. It's not that he's forgotten how to coach like he was coaching last year, he's doing a lot of the same stuff. It's that this year it's being exposed more than it was last year, because the bad shots aren't falling as much as they did last year.
To address TPins, the difference is, when UNC was running freelance under Coach Williams they were moving and setting screens for each, getting good looks. They weren't standing around watching the player with the ball try to create their own shot. How many times do you recall Coach Williams yell "move?" They also pushed it, a lot, running break and secondary break. As mentioned above, the teams under HD are much more stagnant on offense. There's a lot of standing around, watching someone try to create their own shot. And two-man offense - high screens.