Zion is too quick for bigger players, too strong for smaller ones. He presents a matchup problem, where it is a no win situation. I don't really envision Sengun being a guy that is wholly impossible to guard at the NBA level. He just doesn't have that type of unique skillset.
I'll preface this by saying that I don't want this to devolve into a real debate about which one of them was/is a better prospect. We could talk in circles and get nowhere. That said, the dynamic you're talking about here is precisely the dynamic that's making Sengun so dominant in Turkey. He clobbers PFs and small-ball C types, and makes traditional C's look like statues.
To take the comparison just one step further, I want to emphasize one more key thing both of them do, which is that they really consistently punish double teams with their passing. That's what puts defenses in a bind and makes them impossible to defend.
I think Sengun will be a good NBA player but Zion is in another stratosphere analytically. I understand it is pro vs. college but across nearly all dimensions, Zion was the absolutely elite of the elite analytically. Zion, Durant and AD are the only possession era players who had profiles so certain that it would have been impossible to think they wouldn't be stars.
It's interesting that you cite that trio, because those are the 3 freshman Wooden Award winners. Overseas, just one other freshman-age prospect has won league MVP against a comparable or stronger level of play, and that's Luka. So we're 4/4 so far with those ultra-dominant 18 year olds becoming superstars. Now along comes Sengun...
Again, I like Sengun, have trouble figuring out where to slot him.......but even as a great player, at 18, he is not producing across the board, like those
truly elite guys do. Where it looks like they really just have no weaknesses. This will probably devolve in to a pro vs. college debate but.....
The thing that is so next level insanity about Zion is.......lets say you want to try to ball park the reduction in competition, if you want to believe there is a very large one.
I don't think it's a good use of time to go back-and-forth about specific statistics, though I think some, blocks in particular, are a lot easier to come by in the NCAA than in the pros. My claim, though, is that Sengun and Zion are both outliers when it comes to 18-year-old prospects, and pickings are slim if you want comparison points for outliers like that. Even if you loosen the age restriction to allow 19-year-old prospects, Sengun may be more similar to Zion than to anyone else.
You can apply a penalty in this calculation......so even if Zion takes a 20% reduction, he still is a vastly superior guy......and that is just physical traits and defensive profile aside, where Zion (to me) far and away beats Sengun as well. My opinion would be that Zion would dominate the Turkish league the same way he dominated NCAA but we can shelve that for the sake of a 4 page debate.
This should also be the point in time where I also mention I thought RJ Barrett might be a better prospect then Zion, at the start of the 2019 college season, so what do I know. ¯\_(ツ)_/¯
For this, I'm trying to put Zion's NBA success out of my mind and just think about him as a prospect. He wasn't without weaknesses. There were people who thought Ja should go #1. People pointed to Zion's lack of height and shooting ability in particular...hell, people criticized Durant and Luka for perceived physical limitations too. They probably criticized AD for something, though I'm not sure what it was
. No prospect, no matter how dominant, is going to be completely beyond criticism. But at some point you have to just not overthink it and draft the guy.