Again looking solely at the original film, there are only two lines regarding "destiny." The first being Han...
and Ben's
If you are to look solely at Star Wars, Luke's destiny is to be the hero who destroys the Death Star. Luke's father left no journey for him to find his lightsaber. He simply wanted Luke to have it. There's no completely out of the blue suggestion that Vader is Luke's father. There's only the suggestion that he chooses to follow his father's footsteps. If you want to go a step further, what has become known as "the Force theme," John Williams intended only to be Obi-Wan's theme. Now, the Force Theme is synonymous with destiny in the Star Wars universe. But, while important, it meant so much less back looking only at Star Wars.
The concept of destiny is so underplayed in the 1977 film, its a blink and you miss it kind of thing. Again, you're choosing to suggest that destiny plays a bigger role. If that's how you see it, cool. But Lucas was creating modern myth. He was taking bits and pieces from all of these things and in hindsight, absolutely! It's Arthurian legend! But if I am to look solely at the modern myth created by the 1977 version of the film Star Wars, I think he was just borrowing from a lot of sources and creating his own thing. That, to me, does not indicate a destiny more than being the hero in that moment. After, it absolutely grows.
I don't think there's a wrong answer as it really is an interpretation. So I'm happy to agree to disagree here.