Dallas lets Luka have rebounds? That's a bogus argument, how about Luka commands the area more and collects the rebounds. The fact that you argue that Harden has to share the assists with Westbrook shows Luka's importance to the Mavs more, Luka has to be the prime scorer and playmaker, something neither Harden or LeBron have responsibility over.
Once again, the Mavs still do well when Luka sits. The rockets turn into one of the worst teams in the league the moment Harden is not on the court. How is Luka doing more exactly?
Harden averages 38 points while Luka averages almost a 30 point triple double a game! Westbrook won the MVP over a similar 30 point triple double season (though in a less efficient way).
Luka does more on the court than Harden, he's the playmaker and scorer for team that's doing well above expectation
Harden comes ahead on PER, OBPM, RAPTOR, PIM, you name it
He scores more, assists slightly less, loses the ball less, is more efficient. Luka may do more things, but Harden does his better
Also, here's how many players averaged 38 or more in NBA history: Wilt. The end
And again, and i can't believe i have to repeat this: James Harden gets systematically doubled at halfcourt to force the ball out of his hands, and he still averages a 38/5/7 line with the second highest PER ever(only Giannis this season is ahead)