Zion gets a few cool highlight plays a game, but I think we need to tap the brakes with comparisons to the greatest players of all time.
The first warning sign is that Duke did not look dominant in the tournament. Duke has 3 players projected to be in the first 10 picks, and they were a couple of no calls on offensive fouls away from being knocked out the first weekend of the tournament. If Zion was truly a dominant player, he should be able to carry a team as good as Duke to the Final Four by himself.
His height is an issue, and he doesn't make up for it with wingspan. He is 6'7, and his wingspan is 6'10. Most PF's at the next level are 6'10 and 7'2. He is going to try and out-muscle opponents, but NBA 4's are pretty strong.
There only two prior examples that I can think of where an undersized PF became really successful in the NBA are Charles Barkley and Larry Johnson. Larry Johnson feels like the closer comparable to Zion. Johnson was a great athlete that was explosive and bigger players struggled to cover him. Johnson had an advantage over Zion in that there were still some big stiffs at the 4 back then which there aren't now. Johnson didn't get to the NBA until he was 22, but he only had about 5 years at the top before the wear and tear of the NBA caught up to him. Carrying that much weight, even if it is muscle, is a lot of strain on the joints and knees in particular. I feel like Larry Johnson is Williamson's upside.
Barkley was a once in a lifetime player. He was 6'6 and probably played at 250-260 most of his career. He was very skilled, and a very accruate shooter. There wasn't nearly as much 3 point shooting back then, but Barkley had a good mid-range game. He also averaged over 4 apg most of his career. Williamson has a long way to go to be Barkley.