Duval took a lot of heat for his decision making. In this system, Duval was expected to be a 'natural/traditional' pg with a 3pt shot. Duval was a combo guard that did not have an efficient 3pt shot. His facial expressions were at times show his frustration. There were also moments where he needed to be encouraged on the bench.
Many fans became very critical of his play and attitude.
Coming in, Duval was never expected to be a shooter. Everyone knew he couldn't shoot, including K, some though (like myself) thought maybe if he can just be average and be respected from the outside than that will open everything up for our 2 monsters in the middle. Ultimately, he was never respected from the outside (much like Tre Jones this past season) and it made things that much harder for the other 4 guys.
You're exactly right, K's system generally needs the PG to be a shooter, and Duval was the opposite of that.
Immature things like the UNC dunk, the preseason game suspension for skipping class definitely didn't help But IMO the frustration was pretty basic, he was a massive recruit (#3, #4, #5, #7 depending on your service, and on all of them he was the #1 PG in the country.) He was a better rated recruit than Tre Jones. Andddd he could barely stay in the starting lineup. He just didn't live up to the hype, and he definitely could have used a 2nd year in college. He was the classic "destoyed guys in HS by just being way quicker and more athletic than everyone else."
Ironically, Duval was the best Duke player on the floor in the Elite 8 against Kansas. They couldn't guard him, at all.