Jack is just the better boxer all round. Faster hands, much better defense, probably hits harder as well
Sturm is a better all around boxer than Jack and Chudinov outworked him, Chudinov would bring too much pressure, he'd wear down and stop Jack late or outpoint him.
Jack needs someone he can intimidate with his power. He's otherwise a mediocre boxer with a poor work rate. Chudinov would easily decision him with scorecards being probably closer than they should be if the fight is in the states.
