You have to remember Lucas in college was about film without story. He was into the french New wave and something called Cinema Verite where filmed are composed with montage and can resonate themes and ideas with the viewer but often no script is needed or just a bare plot. Lucas never was about story he was always about plot.

I think People got confused because Lawrence Kasden Wrote 2 brilliant scripts with Raiders of the Lost Ark and Empire Strikes back. The Huycks wrote the best dialogue of the first star wars. Lucas credits them with 30% of the final screenplay. Not sure how much of Graffiti is theirs also. I know Walter Murch helped Lucas write THX 1138.

He always had friends helping Him with Scripts Until he made the prequels and Indy 4 he became obstinate and set in his ways that he had to write, edit and direct them himself to not get his vision muddied. He believes Both Kurtz and Kershner ruined and Muddied Empire strikes back.

The idea that a writer, director, editor, and producer all in one the one man filmaker is from the french new wave and they called it auteur theory. Truffeut, Goddard and others followed this.

Now to be Fair to Lucas all his companions have also had their share on failures and flops.

Indiana Jones Temple of Doom, Radioland Murders, and Howard the Duck were written by the Huycks. Kershner ended up directing Never say never again. Kasden never wrote another good script after Empire and Raiders, and ended up later making a bad stephen King movie.

Other than the Dark Crystal and Return to OZ Kurtz went nowhere after he was kicked out of Lucasland.