I’m sorry, what? What exactly is “claustrophobic” about the plot and characters of Star Wars?
And besides that, from where in the Original Trilogy do we learn anything about Han Solo’s backstory? Prior to and during Star Wars, he was a selfish, scoundrelly smuggler; he had unpaid debts to crime lords; and he won the ship he now owns from his old friend, Lando. That’s it. That’s all we ever learn about his pre-OT past from the OT itself. Does that make him any less of a compelling character, especially in the original Star Wars film?
The “claustrophobic” element I refer to is the “popular” reading of the first film, whereby none of the character’s in the film have a literal, familial relationship to Luke, and if any of them do, this somehow ruins the integrity of the film. A reading which was borne out of Lucas having to make the film work as a stand-alone film, something Lucas was forced to deal with due to practical/real-world movie making considerations. *
Notice that I don’t posit that Han or Ben were related to Luke. We are only taking about Vader and Leia here. If Leia being Luke’s sister is universe shrinking, how in the world is Vader being Annikin/Anakin not?
Vader having a secret identity under the mask was not out of storytelling bounds in the least, whether he was Ben’s estranged son, Luke’s older brother, his illegitimate father, Luke’s uncle/Annikin’s (younger?) brother, etc. Leia, otoh, could have been Luke’s “cousin” (iow, the Lar’s child, from the second draft), a half-sister to Luke (but older than him, rather than younger, as the public script implies with their character ages).
*Ben being killed off, the Tarkin/Vader dynamic in terms of the Imperial hierarchy, the implication that the Death Star is the key keeping the Empire under control, are all things that make the first film work on it’s own
edit:
I would say that each film of the OT was designed to work on it’s own (yes, even TESB), as much as and maybe even more so than being designed to work within an overall trilogy/saga.