ATMachine said:

I think Larry Kasdan really ran with the idea of Vader Force-choking underlings at the drop of a hat, to the point where it became a running joke.

However, this is certainly an improvement over the Leigh Brackett draft of the script, where Vader just nonchalantly dismisses stupid officers with lines like "Leave me, you incompetent idiot."

That was probably one reason why Lucas disliked the script--judging by Splinter he was probably much more on board with Kasdan's take.

It is hard to say whether it was Kasdan or actually Lucas. There was one more Lucas' draft in between Brackett and Kasdan.