I think the term universe shrinking can’t really be applied to Star Wars and Empire. What you criticize, is that they don’t establish a very vast universe, but universe shrinking means that the established world is retroactively made smaller. Leia being Luke’s sister has consequences for the other movies before Jedi, while not offering anything interesting to the plot.
First I agree about Leia being the sister not offering anything to the plot of ROTJ. That, for me, is the problem I have with it. Leia’s character doesn’t really change, and her character arc/role in the story seems like the way it would have been had she not been Luke’s sister.
Second, about consequences to the previous two films: so it turned out she wasn’t ‘really’ an Organa. Since Alderaan was conveniently (there I go again) destroyed in the first film, how much would we have really learned about the Organa’s in future Star Wars stories, had Lucas not pursued the sibling angle?
The Yoda subplot is interesting enough on its own, so most people don’t care about the setup being too convenient or not.
Perhaps. And if they do, maybe only in hindsight. And certainly not as an introduction to the series (with SW and ESB being the first films produced and released from the franchise). The only ‘consequence’ that Yoda has for the previous film is for the audience to wonder whether speaking in-universe was Ben/Obi-Wan going to be Luke’s teacher for the long-haul, or was he always intending to have Yoda teach him (had Ben not died/sacrificed himself so early into the franchise?)
One obvious consequence is that if Leia and Luke are siblings, Vader is also Leia’s father. Vader was directly facing her in Star Wars, being near her for a long time while she’s on the Death Star, and he never sensed anything through the force?