When James Cameron was promoting his new docuseries "AMC Visionaries: James Cameron's Story of Science Fiction," Cameron ultimately goes into the detail about the differences between "sci-fi" and "science-fiction." James Cameron commented:
We can see the market drives us to a sort of science fiction now that's either competely escapist and doesn't require a technical consultant - an example of that would be 'Guardians of the galaxy.' It's just fun. We don't care how those spaceships work or any of that stuff works. And then you have scientifically responsible science fiction like 'The Martian' or 'Interstellar.'"
By that logic, Cameron isn't incorrect as there isn't much thinking required for James Gunn's Guardians of the Galaxy. It would also be fair to say that Taika Waititi's Thor: Ragnarok is in the same category as GoTG as they are both classified as "sci-fi" and not "science-fiction."
Both Marvel and DC Comics have had stories in which they are classified as "science-fiction" in their comic stories, however, in terms of their movies they usually stick with the "sci-fi" route and that's mainly because it's more appealing to the audience both companies are targeting.
However, it is interesting to wonder whether Marvel Studios will ever have a movie that sides with a more complex "science-fiction" movie or if they'll always continue with the "sci-fi" route that we've all grown to appreciate.