I think Zion really does have all of the potential in the world. He could end up being a top ten player of all time. For all we know, he could end up being the next Lebron. But acting as if that's guaranteed is ludicrous.
Zion is, like you say, an athletic freak. He's skilled in the post, he's got a good knack for rebounding, he's active on defense, he's a pretty sharp (if a little unimaginative) as a passer, and he's ultra efficient around the rim. All of that is great. If he can carry those skills through into the NBA, and even be average from three, he'll be a top ten player in the league without much issue. The problem is, is that the jump between ''top 10 player'' to ''best player in the league'' is a huge leap. Think about it this way:
Coming into this season, ESPN had Damian Lillard ranked as the 10th best player in the league. Their number 1 was Lebron James. Damian Lillard is amazing. He's got a bunch of skills, a great mindset, he plays hard, he's fearless, and he's got real heart. He's not Lebron James. His career best season doesn't match the worst season Lebron's had in the last decade (this season).
Damian Lillard 2016-17: 27pts, 4.9rbds, 5.9asts, 0.9stls, 0.3blks, 44.4% FG, 37% 3pt, +5 Net Rating, 4.3 BPM, 4.3 VORP, .185 WS/48, 24.1 PER
Lebron James this year: 27.9pts, 8.7rbds, 8.6asts, 1.4stls, 0.6blks, 51% FG, 33% 3pt, +6 Net Rating, 8.1 BPM, 4.9 VORP, .180 WS/48, 25.8 PER
Zion could easily end up being a Damian Lillard caliber player. Maybe he'll end up being an Embiid caliber player. But acting like he's just automatically in that Lebron, KD, Giannis, AD category as a given, before he even plays a single minute of NBA ball, is almost asking for him to disappoint you.