A script is more than just dialogue. Even if the dialogue is 30% Lucas it’s still mostly Lucas’s script.
One thing I that was crucial to the success of Star Wars’s screenplay was the multiple drafts of rewrites that were done not just to improve dialogue, but to streamline, simplify, and strengthen the story. It’s unclear to me how many drafts the PT went through but I strongly suspect there weren’t enough, considering how expansive Lucas’s vision tends to be (McCallum mentions on the commentary for AOTC starting shooting without a finished script, and Lucas talks a lot about various reshoots). This fact hurt the films and made them a little scattershot; but also in general Lucas is, as stated, not great with the human element and his writing struggles when it comes to dialogue but also the specifics beats of what make up character dynamics and character arcs.