This argument is ridiculous. Leia being Luke’s sister is universe shrinkage because they were two separate people with disparate stories and backgrounds that didn’t come together until those fateful events in the original film. Making them siblings causes their backgrounds and stories to come from the same place.
Vader’s story, on the other hand, is already intertwined with that of Luke’s father. Key difference.
The stuff about Yoda doesn’t even make sense.