hand strength is a real issue, but solvable to some extent, Going strong and just clasping that ball hard is something he can work on. Becoming significantly stronger generally will be hard. He can't really gain girth, he is not a bulky or lowerbody strong type of guy, and will probably never be. But anyway it is clear that teams know better how to fight against him, how to make him uncomfortable on O and use his weaknesses in D.
Nevertheless while going through these growing pains and his own form of rookie wall (after having started playing a lot more early 2015 than having had the Euro) he remains a defensive monster, intimidating the crap out of offenses around the league.... And while he will never be Kareem nor Hakeem on O, there is some margin there, we will see where it goes.
Beyond his personal skills and improvement, let's not forget that he is a big guy and big guys are a lot more dependent on the rest of the team to be efficient on O. Maximising how the team uses him, learning how to leverage his size and relative speed, etc... all those things take time but will make a difference. My guess is that we are still looking at a 10/12/2,5 to 3 type of season from him and stats putting him up there as one of the best defenders in the league and close to already being the best defender at his position...
So it's not going to bad as it stands, it's just that we shouldn't think of him as something else as a Mutombo style of player : D is where he will reigns supreme, the O will always be and extra.