Morant is really intriguing, but if you watched the game yesterday, you wouldn't have seen him put any significant energy at all into defense, and was a study in energy conservation. On the other hand, Zion has one of the highest revving motors we've ever seen, and plays intense defense.
Morant clearly picked Marquette apart, but until I see him man up against a pro level point guard, I can't put him at the same level as Zion. Murray state never put him on Markus Howard, so I doubt we see him doing any tough defensive assignments in the tournament.