Disagree here. It's not like "sci-fi" is some squarely fenced off genre of film, you can do many different things within sci-fi. Star Wars is nothing like 2001: A Space Odyssey, which is nothing like Alien, which is nothing like Blade Runner, which is nothing like The War of the Worlds, etc. A compelling argument could even be made that most, if not all, of the MCU is also science fiction as every single film in the MCU deals with sci-fi concepts (suits that make a man stronger, vast galactic societies, magic stones from space, etc.).
If anything bottlenecks Star Wars and the MCU, it's Disney's complete reluctance to do anything interesting or daring with the concepts its been handed. With Star Wars this is very noticable, especially with how they responded to the things The Last Jedi did, but it's also there with the MCU. Even though the MCU dares a little more than current Star Wars, no MCU film really dares to make any radical changes. I mean, I keep seeing people say that the MCU can do stories in 'many different genres', but right now there's not a single MCU film that cannot be described as a 'comedic action blockbuster'.