The most impactful reveal in all of Star Wars history (and honestly, film history) was pretty much pulled directly out of Lucas’ ass VERY late in the game on the second movie alone. It turned his trilogy’s hero into the son of a genocidal fascist, and the most direct representation of evil in action up to that point.
Describing that story as a “relationship” developed over three movies is mostly untrue. There isn’t a relationship AT ALL for most of the first two movies. You only find out there’s a legitimate connection deeper than “You killed my father prepare to die” at the very end of the second movie. The third movie is the one that has to actually develop that relationship into something, and it’s arguable how well that was done. The heroic moment on Vader’s part carries a LOT of that weight.
“Universe shrinkage” ceased being a problem that was ever going to have a solution back in 1999. It’s been 20 years.