Niang was a great collegiate player, the rare 4 year guy that was solid. But Niang didn't have NBA size (for his position), and insane shot (good yes but not insane), or the athleticism/footwork to be a force in the league. Buckets has and all NBA type shot, quicker feet, more length (perimeter playing), and a better midrange game. He's already a better NBA prospect than Niang ever dreamed of being. And that's not a slight on Niang.
As far as passing I don't ever see Milan "needing" to be a great passer. If he's able to get the ball he's likely able to shoot it (and it's likely going in).