The Marvel Cinematic Universe is one of many Marvel story arcs

When people mention the Marvel Cinematic Universe, that is Paramount Studios's story arc of the Marvel comic book universe. However, there are multiple "universes". All of the X-Men movies (including Deadpool) are considered to be in an "alternate universe" because they are produced by 20th Century Fox. Universal Pictures produced The Incredible Hulk in 2008, and Sony was in it's own universe for a while with the Tobey McGuire and Andrew Garfield Spiderman movies. But they partnered with Disney in 2015 to share the rights to Spiderman and the Tom Holland version was then integrated into the Avengers. The Netflix series are considered part of the greater MCU arc as they are also produced by Disney.

Those don't even include the large number of Marvel movies that came out in the 90s. Most of the movies, including Ghost Rider, Daredevil, Elektra, both Hulk movies (the Ang Lee production is like a live comic book!) and a few more have had mixed, if not poor, reviews. However, Kevin Feige who has produced ALL of the MCU titles, has gotten it right pretty much every time. The Marvel Cinematic Universe has been the pinnacle of cinematic domination since 2012 and it doesn't look like it's slowing down any time soon.

"The first film in the Marvel Cinematic Universe was Iron Man (2008), which was distributed by Paramount Pictures. Paramount also distributed Iron Man 2 (2010), Thor (2011) and Captain America: The First Avenger (2011), while Universal Pictures distributed The Incredible Hulk (2008). Walt Disney Studios Motion Pictures began distributing the films with the 2012 crossover film The Avengers, which concluded Phase One of the franchise. Phase Two includes Iron Man 3 (2013), Thor: The Dark World (2013), Captain America: The Winter Soldier (2014), Guardians of the Galaxy (2014), Avengers: Age of Ultron (2015), and Ant-Man (2015).

Captain America: Civil War (2016) is the first film in the franchise's Phase Three, and is followed by Doctor Strange (2016), Guardians of the Galaxy Vol. 2 (2017), Spider-Man: Homecoming (2017), Thor: Ragnarok (2017), Black Panther (2018), and Avengers: Infinity War (2018), with Ant-Man and the Wasp (2018), Captain Marvel (2019), and an untitled Avengers film (2019) still scheduled for the phase. Sony Pictures distributes the Spider-Man films, which they continue to own, finance, and have final creative control over."