So obviously Lucas had a much bigger presence during the making of Jedi than he did Empire, he was practically a Co-Director, but did Marquand leave any mark of his own on the film? I haven’t seen his other work so I can’t say, and I don’t know if Lucas has attempted to erase any sort of legacy Marquand had like he did so many others on the OT.
I think Marquand had pretty much the same role in ROTJ as Kershner had in ESB. In both cases Lucas led the creative part (story, characters, screenplay, world-building, etc.), while Kershner and Marquand led the implementation and contributed in various ways to the creative part. If you look at it like that, then Lucas was “practically a co-director” in both cases.
Like it was pointed out, Marquand had some important contributions to the creative part, besides directing the implementation. Like Kershner, I think he was a valuable part of the trilogy.
Well from what I heard, Lucas was annoyed with alot of the changes and alterations that Kershner made while directing Empire, so for Jedi he was on set way more than he was during Empire and reshot quite a few scenes, apparently the whole reason Jedi was filmed in the United States was so Lucas could be on set daily.