He's never been a great rebounder. Not a big deal with AD/Aminu next to him.
1.7 blocks per game
That's good for 13th in the NBA, with all but 3 guys ahead of him playing more minutes per game, some much more. He has a clear cut/valuable role: start games/2nd halves next to AD, and let AD/Ryno play in crunch time. I don't know what you were expecting from him, he's met/exceed pretty much everyone's expectations.