If you look at every center drafted in the first round over the past 15 years they generally average something in like the 8 ppg 6 rpg 1bpg range (+/- 2 points and rebounds per game). There are exceptions like towns and both okafors but even future elite centers tend to struggle early like gobert, Steven Adams, Al Jefferson, Noah, and so on.
Bamba is going to spend at least the first part of the year learning behind vucevic.
Bamba is joining a team that isnt bottoming out. He's not going to get unlimited usage. He's going to fill a role and play into that role for a while while Fournier, Gordon, Simmons, Ross, and vucevic take shots.
Other players (Trae Young, Kevin Knox, Sexton) are going to have a bigger role on their teams.
We really need to lower expectations for Bamba this year as he doesn't need to get there all at once. A good baseline for first year Bamba should be basic counting stats that exceed what Biyombo did last year (with better advanced stats impact).
That's not to say that's who he'll be as a player, but it is what he should be as a rookie