I like Grant Williams and I want to see him succeed, but I really think that to make it as more than a 9th-10th man in this league he's going to have become a lot more skilled offensively or else miraculously grow several inches.
Same as Draymond Green -- minutes limited his first two years in the league because he could not reliably make a jump-shot. Grant Williams in the same situation. He has to be able to make wide open spot up jump-shots to stay on the court.
Draymond Green could also handle the ball in a pick and roll and regularly forced turnovers.
Grant keeps the ball moving on offense, hands the ball off well, and stays in front of his man on defense.
He doesn't reliably hit shots, doesn't force turnovers, can't handle the ball against defensive pressure, isn't big enough to score on post-ups unless it's against tiny guards ....