Considering Lucas did not even write the dialogue negative 1 is critcising That is not surprising Vaderisnothayden. Willard Huyck and Gloria Katz wrote that. The best dialogue of Empire Strikes Back is Lawrence Kasden.

Lucas had people helping him write the originals when he got to the prequels he pretty much wrote them himself. except for minor rewrites on episode II by Jonathan Hales, and uncredited work by Carrie Fisher on Epsiode 1 being rumored.

Did he write episode III completely by himself?

In his own words Lucas says " I am a terrible writer" he said he "hated directing". Yet he directed and wrote the 3 prequels all on his own because he did not want people muddying his vision Like Kershner did on Empire Strikes back as he has implied but never said directly. He also was not 100% happy with what Marquand gave him on Return of the Jedi. So he decided to have things his way he would have to have all control.

He also says he only got about 20% of the movie he wanted on Star Wars. and something like 40% of what he wanted overall with the oot. with the special editions changes he now says it is closer to 55 or 60% of what he wanted. and he says being unhindred by technology he got 100% of the original movie he wanted star wars to be with the prequels.

So the so called "compromises" and "limited palette" he had on the original trilogy was what made the films better. Because he had to get help from friends and colleagues and look for creative solutions. Digital editing, creating the perfermance afterwards and not getting it from directing the actors, and cgi gave him wooden performances and allowed him to get lazy with cgi. Thereby making the prequels suffer as a result. He shot for keeping things consistant in their mediocrity and succeded.