Sorry Imp, but I don’t think you know too much about this. Kersh didn’t shoot any master shots on Empire, which kept Lucas from fucking up the movie in the editing room. That was the main reason he stood over Marquand’s shoulder the entire time during filming of ROTJ.
I have heard of this “theory” before. There are plenty of master shots in the film, which is obvious proof that this “theory” is false. Anyway, it is not like you just need master shots to play around in the editing room. The amount of different takes is what actually matters. And the reality is that they did so many takes that editing was like playing in a sandbox compared to ANH.
The main reason he stood over Marquand’s shoulder was because he did not want the film to go twice over budget and twice over schedule.