He's rumored to be the best in this draft at reading defenses pre-snap, a quality that is currently lacking even in the NFL and has for some time. He also has really good accuracy and can zip the ball when he wants to, but often chooses to throw "catchable balls". He can also scramble and run well. The knock and the reason he's a late bloomer in draft talk is because a lot of people didn't watch him and see what he was, vs what was happening. Ole Miss had some very terrible play calling and rather then challenge Lane Kiffen, he tried to make the system and play calling work. But it wasn't happening to a high level. The offense was far too devoid of talent. Their Oline was bad. Their RB was always struggling. It was really just Dart, Harris and somewhat Wells Jr making everything happen on offense. And yet they still managed to finish 11th in ranking from it all. Large part due to Dart, Harris and the front 7 on defense keeping the score low enough so an offense devoid of talent could make things happen (which Dart did despite the offense lacking talent and bad play calling).
There's a decent chance here that if an offensive genius similar to Payton gets their hands on him at the NFL level, he could be better than Bo Nix.