Not really. Both those guys could get massive if they wanted to just focus on getting big and ripped for the "look", but it's not productive. They are both better athletes than Niang. They arent better because they work harder on it, it's just genetics. And getting bigger/stronger/faster is mostly about endurance rather than peak play. Players are working on their body so they can play at a high level for longer more than it is about getting 20% faster or w/e
Donovan talked about how he was eating an entire pizza after practices at Louisville and how when he mostly ate out at Ruth Chris and The Cheesecake Factory his rookie year.
You have to be a pretty special athlete to hold onto muscle in the NBA. Most of these guys arent lifting year round (I think some bigs do). Niang just has a body type that holds onto body fat more easily and doesn't retain muscle as easily.