I think Miles and another year of development makes them better. Also, don't be shocked if simply not having Carroll and PPat forces Casey into player usage that makes us better by default. Norm's length allows him to guard some small forwards in today's NBA and I wouldn't be remotely shocked if more Siakam, more Norm and Miles's shooting gives us a huge upgrade at the 3 overall.
Basically, I think Casey's insistence on playing "the veterans" who were complete black holes offensively actually hurt the team last year. It's not like he was playing Carroll and PPat in defensive specialist type minutes and situations. They were playing 6th-7th man type minutes, and getting the same type of FGA as Val and Norm were getting. Moving them out and letting the best of the kids fill those roles and take those shots improves us.
The kids are also loooong. Norm has a freak wingspan (6'11 I think, for a 6'4 guard), Siakim has a 7'3 wing span, Delon has a freak wingspan for a PG, Bebe is Bebe. They can all get after it defensively to replace what we're supposed to be losing from the veteran exits and bring more skill offensively.