Duke did not win a national title this year because their roster was flawed.
Even though they had a ton of top end talent, that talent did not necessarily fit together well on the court. Reddish and Barrett played the same position, and would have had similar roles had they been on different teams. On the same team, Reddish was often the odd man out. Even still, Reddish was easily their third best player.
Behind the four freshmen (adding in PG Jones) Duke had basically zero depth. The NCAA is still five on five, and Duke didn’t really have anyone else they trusted to give minutes to. Their four freshmen all played about 30 mpg, with most of the other players on the team playing 20 mpg or less. Had Williamson, Reddish and Jones not missed time, there’s a decent chance that Duke would have had four players average 30+ minutes and four others averaging 15 or so minutes per game. That lack of depth consistently got exposed, particularly in the tournament where good teams could attack the weak link on the floor.
On top of that, Duke didn’t have much in the way of perimeter shooting. They shot 30% as a team from three. They likely would have been unguardable if they had shot 35% from three, and a real nightmare at just 33%.
Duke had a flawed roster and it haunted them all March. If you could keep Williamson and Barrett out of the paint, Duke was actually easier to guard, and they always had at least one weaker player on the floor.
We all know that most NCAA champions have at least seven or eight legitimate contributors. That is just a must unless you get really lucky.