People seem to forget lucas only directed ANH and the shitty prequels.
Still, he was the primary author behind the other two.
“Story by:…” and special effects are what he was good at (and darn good at). He should have stuck to those and let other people write the script, direct, etc.
His main attribute is definitely creating stuff/ideas. I think he is good screenplay writer, it is just that someone has to fix his dialogue.