Well, it's true that Magic didn't lead the team in all of these areas but then again, he was playing with Jabbar, Nixon and Wilks so there was a decent amount of veteran talent on that team who could really score.
Jabbar would have been interesting to watch play in the NBA at the age of 20. Of course, he wasn't able to, as were many of the older greats. They didn't have any hardship rules back then so between not even being able to play on the varsity college team as a Freshman and not being able to enter the NBA early, many of those guys were there for the full 4 years and then entered the league.
Doncic could be the best but we also have to remember that the NBA is not the first Pro league that Doncic has played in. He was in the Euro League before ever coming into the NBA, if I'm not mistaken.
If I had to pick, I'm taking James all day at 20 but that's just my opinion.