I also think that just in general, as elite athletes age, they do themselves a favor to slim down. Look at Lebron. I don't remember what year it was, but one off-season in particular, he cut a bunch of weight and his game seemed to just kick into another gear that he didn't have before.
I think Tom Brady is another that played better as he cut weight.
I think if Zion Williamson wants to help himself out, he'd slim down over the upcoming season. Maybe he's a bad example, because it's always been obvious for him.
I know KVN was probably asked to bulk up earlier in his career, but seeing him look more like BYU KVN is refreshing and seems more sustainable, even if he only has a season or two left in the tank.