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.