^ Your point about the “I am your father” plot twist having little effect on the overall screen play is important.
This ties into another issue I’ve always had with Empire Strikes Back, even the final version. (Obligatory qualifier: the final version of ESB is one of the few films I’ve seen that comes close to being a “perfect” movie, so my criticism here is less about the quality of the script/film and more an attempt to make sense of Lucas’ thought process regarding Vader in relation to the rest of the film.)
One thing that always (slightly) bothered me about ESB is that Vader’s motivations - and how they tie in with his actions throughout the film - always seemed a bit “off”, and the reason for this I think connects back to the insight that the “BIG REVEAL” at the end has little effect on the rest of the movie. We can start with a simple question, often seen around the Internet on Quora or various fan sites: “Why is Vader so eager to catch the Millennium Falcon?”
At first, the question seems really stupid. I mean duh… it’s the ship that destroyed the Death Star, right? But Vader isn’t really after the Falcon - he’s after Luke. But Luke’s not on the Falcon. Okay, well Vader doesn’t know that, so Vader is just pursuing the Falcon because he knows the ship is at least connected to Luke, so it’s his only lead. Okay, makes sense.
But wait…
Why is Vader so interested in catching Luke? Again, at first the question seems stupid and obvious. But that’s only because we view the movie with all the foreknowledge and surrounding context of the entire saga. In 1980, when people first saw the film, they first find out Vader is after Luke in the very first scene introducing Vader and his awesome fleet. Vader sees some drone footage of a power generator on Hoth, and says “That’s it. The Rebels are there. And I’m sure Skywalker is with them.”
So this would lead to what I’ll call the “DEFAULT INTERPRETATION”: the default interpretation that a typical 1980s movie goer would assume, which is Vader just wants to kill Luke Skywalker, because Luke Skywalker is an obnoxious rebel terrorist that blew up the Death Star. Very simple, straightforward motivation. The DEFAULT INTERPRETATION is from the perspective of a 1980 moviegoer who is watching for the first time, and doesn’t yet know that Vader is Luke’s father.
With this simple “default interpretation” in mind, the whole Hoth invasion sequence makes sense. Vader’s plan is to drop out of hyperspace, and destroy the Rebel base before they have a chance to turn on their deflector shields. This means Skywalker will be killed, along with all the other Rebels. But Vader hits a snag. Admiral Ozzel comes out of hyperspace incorrectly (the logistics of this are obscure), giving the Rebels the time/opportunity to raise the shields. Vader is pissed, because now he has to go through the hassle of a ground invasion. So he kills Ozzel, promotes Piett, and tells Piett to have General Veers prepare ground troops for an invasion.
So far everything makes sense. Then after the Battle of Hoth happens, and Vader is in pursuit of the Falcon, he gets an incoming transmission from his boss, the Emperor. The Emperor tells him that Luke Skywalker is a significant threat. Vader responds: “he’s just a boy.” Then the Emperor expresses interest in converting Luke to the Dark Side. At this point, under the DEFAULT INTERPRETATION (i.e. from the perspective of a 1980 movie goer), there is NO “Sith Rule of Two” subtext going on here, or any deeper subtext about how Vader really feels about his son, and how the Emperor may suspect some disloyalty, etc. There is NONE of that. There is just the idea that Vader thinks “well, I fucked up at Hoth and didn’t kill Skywalker, and my boss is probably mad now. But at least I can keep my boss happy by capturing Skywalker alive.”
Vader then attempts to do just that: he tracks down the Falcon, tortures Han, and lures Luke to Bespin so he can convert Luke to the Dark Side. All of this happens pretty much exactly the same in both Brackett’s draft and the later drafts.
Then we get the “BIG reveal” in Cloud City.
Now, the “DEFAULT INTERPRETATION” is shattered. But when we retroactively apply this new revelation backwards through the script, as the new interpretation ripples over each scene, it creates a LOT of new questions and makes some of Vader’s actions very hard to explain.
Like… when did Vader discover Luke was his son? Was it through his brief conversation with the Emperor? That seems plausible, because before that conversation, Vader was ready to carry out an ORBITAL BOMBARDMENT to instantly kill ALL the Rebels on Hoth. It was only Admiral Ozzel’s incompetence that forced Vader to carry out a ground assault. (Even without Ozzel’s fuck up, the rebels would have been prepared because they found the probe droid, but Vader doesn’t know this.) And even during the ground assault, Imperial troops are just indiscriminately killing everyone - they could easily have killed Luke if he wasn’t lucky. And Vader KNEW Skywalker was on the base way before he spoke with the Emperor in the asteroid field.
We don’t know if Vader knew Skywalker was his SON at that point. (Some Boba Fett comic tells us Vader knew Luke was his son way before Hoth, but that’s irrelevant.) But presumably even if Vader knew Luke was his son at that point, his plan was still to KILL him via orbital bombardment - NOT convert him, nor secretly train him to overthrow the Emperor. And what about the fact that Luke’s last name is “Skywalker”? Even if Vader didn’t know for certain that Luke was his son, the fact that he stumbled upon a force sensitive young teenager with the last name “Skywalker” who hangs out with Obi-Wan Kenobi should DEFINITELY have been setting off alarm bells in Vader’s mind. At the very least, Vader should be thinking: “This needs further investigation.”
Yet Vader is happy to just instantly vaporize everyone on Hoth, including Luke. Then during and after the Battle of Hoth, the Falcon manages to escape, and for some reason Vader zeroes in on THAT particular little Correllian freighter, out of ALL the other countless ships that escaped. Why? Is it because that ship was directly involved in destroying the Death Star? Maybe, but probably it’s just that the Falcon was his best lead at finding Luke, and its hyperdrive was conveniently broken. But until Vader talks with the Emperor (which happens mid-way through the asteroid chase sequence), we can only assume that Vader’s current plan is to find and KILL Luke Skywalker. (And this fits perfectly with the DEFAULT INTERPRETATION).
Now, there’s sort of a “head-canon” version of these events that we probably all have in our heads, from 40+ years of ESB floating about in the public consciousness, and merging with later context from subsequent movies. I’ll call this the “POST-FACTO INTERPRETATION”. The “post-facto interpretation” is: “At some point before ESB, Vader learned he had a son named Luke (possibly from hiring Boba Fett to investigate). Vader then had the idea to use Luke to overthrow the Emperor, which is why Vader is a bit cagey when speaking to Palpatine about Luke. That’s why Vader was so committed to finding Luke, and why he was chasing the Falcon throughout the film. His goal was to confront or capture Luke, turn him to the Dark Side, and then team up to overthrow the Emperor. During the asteroid chase, Vader discovered that the Emperor was probably on to him, but Vader played dumb. Ultimately, Vader’s plan failed when Luke ostensibly committed suicide on Bespin.”
Unfortunately, the actual film does NOT support this “head-canon” or “post-facto” version of events, because we know that Vader was happy to simply vaporize Luke from orbit, along with all the other Rebels, via an orbital bombardment, at the beginning of ESB - after Vader explicitly mentioned that “Skywalker” was on the base. It was only after the orbital bombardment failed due to Ozzel’s blunder, that Vader seemed to switch from “kill mode” to “capture mode”.
The point of this lengthy post is just to highlight how the “big reveal” about “Father Vader” was a very last-minute addition to all this, because it doesn’t really fit logically into the mechanics of the script. It was sort of clumsily dropped into the script, without ironing out all the ripples caused by the addition. It makes little sense that Vader would want to KILL Luke on Hoth, unless we are viewing the movie through the lens of the “DEFAULT INTERPRETATION” - which is how the script was originally written.
Even if Lucas was toying with the idea of “Father Vader” before Brackett wrote her draft, the idea was still sort of clumsily forced into the script, giving the impression of a “last minute rewrite”. The fact that Vader apparently is okay with KILLING Luke at the beginning of ESB is a vestigial remnant of the original script, where Vader very much explicitly really did want to murder Luke: there’s a scene where Vader tries to force choke Luke to death as Luke escapes Hoth in his X-wing. This early motivation partially carries over into the final draft, when Vader orders the orbital bombardment; Vader’s actions were never properly updated to reflect the later revelation at the end.
TLDR:
The original arc for Vader’s motivation was: “(1) Find and kill Luke, (2) Change of plans: capture and convert Luke to appease the Emperor”
The UPDATED motivation in later drafts was: “(1) Find and kill Luke, (2) Change of plans: capture and convert Luke because Luke is his SON, and can be used to overthrow the Emperor.”
But in everyone’s head-canon, the motivation is more like “(1) Discovers Luke is his son, but hides this from the Emperor, (2) tries to capture Luke to overthrow the Emperor”
The head-canon version at some point became ACTUAL canon via some Boba Fett comics. The head-canon version also makes the most sense given the “big reveal” at the end of ESB, as well as the wider context of Star Wars lore. But the head-canon version just is NOT supported by the first act of the actual movie.