Well, one could argue that pretty much anyone other than George could have done a better job directing the prequels. There are many scenes that really look like they were shot in only one take. George was too eager to shoot fast and go play with his computers I think.

Reading the "Making of ESB" book, and in particular the part about the carbon freezing chamber scene you can see just how much thought Keshner put into the movie. I doubt good old George put one tenth as much thought on any scene for the prequels, other than to make it look cool to sell toys.

On the other hand, Kershner was working with sets, props and actors. The rebel base, Dagobah, the carbon freezing chamber all were real. Could he have adapted to the "nothing but blue screen" sets?? I'm talking about stuff like Geonosis, the scene with Mace Windu leaving a Gunship for example. Nothing was there, and I doubt Kershner would have made much difference there.