Amile, Harry, Jeter (a very good per 40 rebounder, maybe Marques). On top of that, your basis of Luke and Grayson's inability is based off of one season, a season in which Duke stayed in the top 10 in the nation in offensive efficiency.
Let's continue, Luke handled the ball enough at the end of the season to instill confidence moving forward, another reason why Duke isn't even sniffing at PG recruits or grad school transfers. Let's not forget Luke's 2/1 assist to turnover ratio. Pretty good for a backup.
Offense is not and aside from one or two seasons in the past 20 years, will not ever be the problem. It's the defense. Can Grayson guard PG's? He would certainly hold a nice advantage at 6'5 with decent lateral quickness. Luke is in the same boat. Will they even have to? Can we get the post help inside to help curb drives?
This year's team, despite lacking a traditional "Duke PG" was offensively brilliant, but lacked rebounding and defense. With some added length and interior size and depth can we be better? The consensus everywhere but on this board, for some reason, is pretty high on Duke's national title prospects.