He pulled down 8.9 rebounds per game last year, so that's probably not too much of a concern.
I think he's overall a smart player. Plus, if he is anything like his brother, he is a good kid, a hard worker, a team player, and an overall nice player. I would much rather take a chance on such a player with the 24th pick, than one with more question marks.
As to need, Barnes and Lyels are FA. Sasha is not yet signed, and will also be untested in the NBA. While I certainly expect Monte to likely bring them all back/over, or find suitable replacements, there are no guarantees till the deal is signed.
In either case, team, ownership, management, and fans, all expect the team to make a deeper PO run next year. I don't expect the rookies (except Sasha) to get much time. This is a question of longer term need/fit. Even if Barnes is back, we will need his replacement in couple of years.
We don't have a FRP next year, and once Domas is extended, no money to get a good wing. A good pick now, with couple of years of development can take major minutes from Barnes. One can argue that there are better options than Kris, but we will need more than defense and rebounding in a couple of years. We'll also need scoring, particularly from outside.