I don't think I've ever seen anyone accuse STAR WARS of being a Dune ripoff. In fact, I can't really see that at all.
It's too bad Frank Herbert isn't still alive, he could explain it to you in person.
Frank talked about this in one of his books. He found 14 separate plot points that were obviously stolen ideas. There is no question that Star Wars was a mixture of Dune and the Hidden Fortress.
The David Lynch movie did not follow the original book exactly because of time constraints, but Frank was a part of the production and was on the set.
He was happy with how the movie was being made. (He passed on before it was finished.)
Desert planet, teenage boy is related to evil lord and the emperor, (a mystery later revealed in the story), boy joins mysterious group of religious warriors who all fight with special edged weapons, these warriors can control others with their voices, the mother of special twins dies giving birth, a giant worm with a human face, on and on it goes.
Even some of the text was ripped off.
That symbiotic circle thing comes from the Bene Gesserit
"Your mind controls your reality" is also a Bene Gesserit lesson.
The term 3-PO, in Dune, meant an artificial person
I look at Star Wars as "Dune for kids"