I'm curious as to what your definition of sci-fi is because both
Guardians of the Galaxy and
Star Wars are both generally considered sci-fi. The Britannica entry is fairly long, but it specifically mentions Star Wars.
science fiction - SF cinema and TV
They're action/adventure movies that happen to have sci-fi elements in them - you could strip out all those sci-fi elements from the story and replace them with swords and wizardry and they'd still be essentially the same movies.
I tend to delineate between movies/fiction whose stories simply happen in a sci-fi-type setting (
The Seven Samurai,
The Magnificent Seven and
Battle Beyond the Stars are quite literally all the same movie with different props...) and those for whom the sci-fi elements are an essential part of the story. The differences between
Star Wars and
Star Trek are a good example...
While the original
Star Trek series may have started out as "
Wagon Train in space", it quickly becomes apparent that a great many of the stories told in that setting simply don't work without the use of "science" and the physics of the universe. They're essential story elements - either as obstacles/challenges, as solutions to those obstacles/challenges, or sometimes even as actual characters in the stories. In every episode and movie, as soon as a new sci-fi element arises that the audience hasn't encountered before there's always a character who steps into the role of the Greek chorus, providing exposition which explains to the audience why that element is important to the story. As early as the first season of the original show we start getting in-setting explanations for a lot of the technology and that information later becomes something that the characters interact with in other stories. The warp core isn't just some "spaceship engine" -
how it works is regularly used as a story element. You go from learning that it requires dilithium crystals to run, to the fact that it can overload for various reasons, to having to eject said warp core to save the ship, all the way to ejecting the warp core being used as a tactic to win a battle. And those dilithium crystals themselves become story elements on their own outside of the warp core - they're more than just "spaceship gas". There's a progression (across multiple movies and tv series) that goes far beyond just "Because... warp core".
In Star Wars, the Force is a major element of the setting and yet the franchise existed for about thirty years before it was defined/explained (at least officially) as anything other than "space magic" (there was a What, but no How or Why), at which point we got a three-minute scene about "midichlorians"... The majority of the in-setting technical information about things like lightsabers, blasters and how spaceships fly was bolted on as aftermarket parts that rarely, if ever, have any real interaction with (and more importantly, lasting impact on) the main plot of the story. In rpg terms it's mostly just fluff rather than crunch. As an example, the important thing to the story is that Count Dooku is supposed to be a legendary lightsaber fencing master, in order for him to be seen as a threat capable of fending off two Jedi masters at once. However, although it's been a while since I watched the movie, I'm pretty sure it's only mentioned once or twice how he became one beyond simply having once been a Jedi. And you don't really need to know that in order to understand his place in the film. Although in the expanded universe beyond the films you know that his fighting style has a name, that it's one of the seven lightsaber fighting disciplines, and that it's the reason his lightsaber has a cool shape to its handle, none of that information has any actual impact on the main story or his place in it.
I think that this divide can best be described as Science Fiction vs. Science Fantasy, in most cases.
Pretty much - I personally see a difference between Lord of the Rings/Western/Buddy Cop Movie/Heist Movie...in Spaaaace! and actual science fiction where specific science/technology/in-setting conceits are integral to (or at least noticeably influential on) the main plot of the story rather than just being used as simple pretexts or set dressings.
